Magnetic tape, magnetic tape cartridge, and magnetic tape device

ABSTRACT

The magnetic tape includes a non-magnetic support, and a magnetic layer containing a ferromagnetic powder, in which an edge portion Ra which is an arithmetic average roughness Ra measured at an edge portion of a surface of the magnetic layer is 1.50 nm or less, a central portion Ra which is an arithmetic average roughness Ra measured at a central portion of the surface of the magnetic layer is 0.30 nm to 1.30 nm, and a Ra ratio (central portion Ra/edge portion Ra) is 0.75 to 0.95.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese Patent Application No. 2021-156586 filed on Sep. 27, 2021. The above application is hereby expressly incorporated by reference, in its entirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape, a magnetic tape cartridge, and a magnetic tape device.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recording media and disk-shaped magnetic recording media, and tape-shaped magnetic recording media, that is, magnetic tapes are mainly used for data storage such as data back-up or archives (for example, see JP2016-524774A and US2019/0164573A1).

SUMMARY OF THE INVENTION

The recording of data on a magnetic tape is normally performed by causing the magnetic tape to run in a magnetic tape device and causing a magnetic head to follow a data band of the magnetic tape to record data on the data band. Accordingly, a data track is formed on the data band. In addition, in a case of reproducing the recorded data, normally, the magnetic tape is caused to run in the magnetic tape device and the magnetic head is caused to follow the data band of the magnetic tape, thereby reading data recorded on the data band.

In order to increase an accuracy with which the magnetic head follows the data band of the magnetic tape in the recording and/or the reproducing, a system that performs head tracking using a servo signal (hereinafter, referred to as a “servo system”) is practiced.

In addition, it is proposed that dimensional information of a magnetic tape during running in a width direction (contraction, expansion, or the like) is obtained using the servo signal and an angle for tilting an axial direction of a module of a magnetic head with respect to the width direction of the magnetic tape (hereinafter, also referred to as a “head tilt angle”) is changed according to the obtained dimensional information (see JP6590102B and US2019/0164573A1, for example, paragraphs 0059 to 0067 and paragraph 0084 of JP6590102B). During the recording or the reproducing, in a case where the magnetic head for recording or reproducing data records or reproduces data while being deviated from a target track position due to width deformation of the magnetic tape, phenomenons such as overwriting on recorded data, reproducing failure, and the like may occur. The present inventors consider that changing the head tilt angle as described above is one of a unit for suppressing the occurrence of such a phenomenon.

For example, assuming that the head tilt angle is changed as described above, it is desirable that running stability of the magnetic tape is high, in a case of recording and/or reproducing data at different head tilt angles. It is considered that the high running stability of the magnetic tape can lead to, for example, the further suppressing of the occurrence of the phenomenon described above.

Meanwhile, in recent years, magnetic tapes may be used in temperature and humidity managed data centers.

Meanwhile, in the data center, power saving is necessary for reducing the cost. For realizing the power saving, it is desired that the management conditions of an use environment of the magnetic tape in the data center can be relaxed compared to the current state, or the managing may not be necessary.

However, it is also assumed that, in a case where the management conditions of the use environment are relaxed or not managed, the magnetic tape is used, for example, in a high temperature and low humidity environment. Accordingly, a magnetic tape having excellent running stability in a case of recording and/or reproducing data at different head tilt angles in a high temperature and low humidity environment is desirable.

One aspect of the present invention is to provide a magnetic tape having excellent running stability in a case of recording and/or reproducing data at different head tilt angles in a high temperature and low humidity environment.

According to an aspect of the invention, there is provided a magnetic tape comprising: a non-magnetic support; and a magnetic layer containing a ferromagnetic powder, in which an edge portion Ra which is an arithmetic average roughness Ra measured at an edge portion of a surface of the magnetic layer is 1.50 nm or less, a central portion Ra which is an arithmetic average roughness Ra measured at a central portion of the surface of the magnetic layer is 0.30 nm to 1.30 nm, and a Ra ratio (central portion Ra/edge portion Ra) is 0.75 to 0.95.

In one embodiment, the magnetic tape may further include a non-magnetic layer containing a non-magnetic powder between the non-magnetic support and the magnetic layer.

In one embodiment, the non-magnetic powder may contain a Fe-based inorganic oxide powder having an average particle volume of 2.0×10⁻⁶ μm³ or less.

In one embodiment, the non-magnetic powder may contain carbon black having a pH of 5.0 or less.

In one embodiment, a standard deviation of curvature of the magnetic tape in a longitudinal direction may be 5 mm/m or less.

In one embodiment, the magnetic tape may include a back coating layer containing a non-magnetic powder on a surface side of the non-magnetic support opposite to a surface side provided with the magnetic layer.

In one embodiment, the magnetic tape may have a tape thickness of 5.2 μm or less.

In one embodiment, a vertical squareness ratio of the magnetic tape may be 0.60 or more.

According to another aspect of the invention, there is provided a magnetic tape cartridge comprising the magnetic tape described above.

According to still another aspect of the invention, there is provided a magnetic tape device comprising the magnetic tape.

In one embodiment, the magnetic tape device may further comprise a magnetic head, the magnetic head may include a module including an element array having a plurality of magnetic head elements between a pair of servo signal reading elements, and the magnetic tape device may change an angle θ formed by an axis of the element array with respect to a width direction of the magnetic tape during running of the magnetic tape in the magnetic tape device.

According to one aspect of the present invention, it is possible to provide a magnetic tape having excellent running stability in a case of recording and/or reproducing data at different head tilt angles in a high temperature and low humidity environment. In addition, according to one aspect of the invention, it is possible to provide a magnetic tape cartridge and a magnetic tape device including the magnetic tape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an example of a module of a magnetic head.

FIG. 2 is an explanatory diagram of a relative positional relationship between a module and a magnetic tape during running of the magnetic tape in a magnetic tape device.

FIG. 3 is an explanatory diagram of a change in angle θ during the running of the magnetic tape.

FIG. 4 is an explanatory diagram of a curvature of a magnetic tape in a longitudinal direction.

FIG. 5 shows an example of disposition of data bands and servo bands.

FIG. 6 shows a servo pattern disposition example of a linear tape-open (LTO) Ultrium format tape.

FIG. 7 is an explanatory diagram of a method for measuring the angle θ during the running of the magnetic tape.

FIG. 8 is a schematic view showing an example of the magnetic tape device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Magnetic Tape

An aspect of the invention relates to a magnetic tape including a non-magnetic support, and a magnetic layer containing a ferromagnetic powder. An arithmetic average roughness Ra measured at an edge portion of a surface of the magnetic layer is referred to as an edge portion Ra, and an arithmetic average roughness Ra measured at a central portion of the surface of the magnetic layer is referred to as a central portion Ra. In the magnetic tape described above, the edge portion Ra is 1.50 nm or less, the central portion Ra is 0.30 to 1.30 nm, and a Ra ratio (central portion Ra/edge portion Ra) is 0.75 to 0.95. In the invention and the specification, the “surface of the magnetic layer” is identical to a surface of the magnetic tape on the magnetic layer side.

Description of Head Tilt Angle

Hereinafter, prior to the description of the magnetic tape, a configuration of the magnetic head, a head tilt angle, and the like will be described. In addition, a reason why it is considered that the phenomenon occurring during the recording or during the reproducing described above can be suppressed by tilting an axial direction of the module of the magnetic head with respect to the width direction of the magnetic tape while the magnetic tape is running will also be described later.

The magnetic head may include one or more modules including an element array including a plurality of magnetic head elements between a pair of servo signal reading elements, and can include two or more modules or three or more modules. The total number of such modules can be, for example, 5 or less, 4 or less, or 3 or less, or the magnetic head may include the number of modules exceeding the total number exemplified here. Examples of arrangement of the plurality of modules can include “recording module-reproducing module” (total number of modules: 2), “recording module-reproducing module-recording module” (total number of modules: 3), and the like. However, the invention is not limited to the examples shown here.

Each module can include an element array including a plurality of magnetic head elements between a pair of servo signal reading elements, that is, arrangement of elements. The module including a recording element as the magnetic head element is a recording module for recording data on the magnetic tape. The module including a reproducing element as the magnetic head element is a reproducing module for reproducing data recorded on the magnetic tape. In the magnetic head, the plurality of modules are arranged, for example, in a recording and reproducing head unit so that an axis of the element array of each module is oriented in parallel. The “parallel” does not mean only parallel in the strict sense, but also includes a range of errors normally allowed in the technical field of the invention. For example, the range of errors means a range of less than ±10° from an exact parallel direction.

In each element array, the pair of servo signal reading elements and the plurality of magnetic head elements (that is, recording elements or reproducing elements) are usually arranged to be in a straight line spaced apart from each other. Here, the expression that “arranged in a straight line” means that each magnetic head element is arranged on a straight line connecting a central portion of one servo signal reading element and a central portion of the other servo signal reading element. The “axis of the element array” in the present invention and the present specification means the straight line connecting the central portion of one servo signal reading element and the central portion of the other servo signal reading element.

Next, the configuration of the module and the like will be further described with reference to the drawings. However, the embodiment shown in the drawings is an example and the invention is not limited thereto.

FIG. 1 is a schematic view showing an example of a module of a magnetic head. The module shown in FIG. 1 includes a plurality of magnetic head elements between a pair of servo signal reading elements (servo signal reading elements 1 and 2). The magnetic head element is also referred to as a “channel”. “Ch” in the drawing is an abbreviation for a channel. The module shown in FIG. 1 includes a total of 32 magnetic head elements of Ch0 to Ch31.

In FIG. 1 , “L” is a distance between the pair of servo signal reading elements, that is, a distance between one servo signal reading element and the other servo signal reading element. In the module shown in FIG. 1 , the “L” is a distance between the servo signal reading element 1 and the servo signal reading element 2. Specifically, the “L” is a distance between a central portion of the servo signal reading element 1 and a central portion of the servo signal reading element 2. Such a distance can be measured by, for example, an optical microscope or the like.

FIG. 2 is an explanatory diagram of a relative positional relationship between the module and the magnetic tape during running of the magnetic tape in the magnetic tape device. In FIG. 2 , a dotted line A indicates a width direction of the magnetic tape. A dotted line B indicates an axis of the element array. An angle θ can be the head tilt angle during the running of the magnetic tape, and is an angle formed by the dotted line A and the dotted line B. During the running of the magnetic tape, in a case where the angle θ is 0°, a distance in a width direction of the magnetic tape between one servo signal reading element and the other servo signal reading element of the element array (hereinafter, also referred to as an “effective distance between servo signal reading elements”) is “L”. On the other hand, in a case where the angle θ exceeds 0°, the effective distance between the servo signal reading elements is “L cos θ” and the L cos θ is smaller than the L. That is, “L cos θ<L”.

As described above, during the recording or the reproducing, in a case where the magnetic head for recording or reproducing data records or reproduces data while being deviated from a target track position due to width deformation of the magnetic tape, phenomenons such as overwriting on recorded data, reproducing failure, and the like may occur. For example, in a case where a width of the magnetic tape contracts or extends, a phenomenon may occur in which the magnetic head element that should record or reproduce at a target track position records or reproduces at a different track position. In addition, in a case where the width of the magnetic tape extends, the effective distance between the servo signal reading elements may be shortened than a spacing of two adjacent servo bands with a data band interposed therebetween (also referred to as a “servo band spacing” or “spacing of servo bands”, specifically, a distance between the two servo bands in the width direction of the magnetic tape), and a phenomenon in that the data is not recorded or reproduced at a part close to an edge of the magnetic tape can occur.

With respect to this, in a case where the element array is tilted at the angle θ exceeding 0°, the effective distance between the servo signal reading elements becomes “L cos θ” as described above. The larger the value of 0, the smaller the value of L cos θ, and the smaller the value of θ, the larger the value of L cos θ. Accordingly, in a case where the value of θ is changed according to a degree of dimension change (that is, contraction or expansion) in the width direction of the magnetic tape, the effective distance between the servo signal reading elements can be brought closer to or matched with the spacing of the servo bands. Therefore, during the recording or the reproducing, it is possible to prevent the occurrence of phenomenons such as overwriting on recorded data, reproducing failure, and the like caused in a case where the magnetic head for recording or reproducing data records or reproduces data while being deviated from a target track position due to width deformation of the magnetic tape, or it is possible to reduce a frequency of occurrence thereof.

FIG. 3 is an explanatory diagram of a change in angle θ during the running of the magnetic tape.

The angle θ at the start of running, θ_(initial), can be set to, for example, 0° or more or more than 0°.

In FIG. 3 , a central diagram shows a state of the module at the start of running.

In FIG. 3 , a right diagram shows a state of the module in a case where the angle θ is set to an angle θ_(c) which is a larger angle than the θ_(initial). The effective distance between the servo signal reading elements L cos θ_(c) is a value smaller than L cos θ_(initial) at the start of running of the magnetic tape. In a case where the width of the magnetic tape is contracted during the running of the magnetic tape, it is preferable to perform such angle adjustment.

On the other hand, in FIG. 3 , a left diagram shows a state of the module in a case where the angle θ is set to an angle θ_(e) which is a smaller angle than the θ_(initial). The effective distance between the servo signal reading elements L cos θ_(e) is a value larger than L cos θ_(initial) at the start of running of the magnetic tape. In a case where the width of the magnetic tape is expanded during the running of the magnetic tape, it is preferable to perform such angle adjustment.

As described above, the change of the head tilt angle during the running of the magnetic tape can contribute to prevention of the occurrence of phenomenons such as overwriting on recorded data, reproducing failure, and the like caused in a case where the magnetic head for recording or reproducing data records or reproduces data while being deviated from a target track position due to width deformation of the magnetic tape, or to reduction of a frequency of occurrence thereof.

Meanwhile, the recording of data on the magnetic tape and the reproducing of the recorded data are performed by bringing the surface of the magnetic layer of the magnetic tape into contact with the magnetic head and sliding. The inventors considered that, during such sliding, in a case where the head tilt angle changes, a contact state between the magnetic head and the surface of the magnetic layer can change and this can be a reason of a decrease in running stability. Specifically, the inventors surmised that, in a case where the contact state between the surface of the magnetic layer of the magnetic tape and the magnetic head (for example, a contact state between a portion near an edge of the module of the magnetic head and the edge portion of the surface of the magnetic layer) changes greatly depending on the difference in the head tilt angle, the running stability decreases and such decrease in running stability can become more remarkable in a high temperature and low humidity environment. However, the present invention is not limited to the inference of the inventors described in the present specification.

Based on the surmise described above, the present inventors conducted intensive studies. As a result, the inventors newly found that, regarding surface properties of the surface of the magnetic layer of the magnetic tape, by making a surface roughness of the edge portion rougher than a surface roughness of the central portion, specifically, by setting each of the edge portion Ra, the central portion Ra, and the Ra ratio (central portion Ra/edge portion Ra) to be within the ranges described above, it is possible to improve the running stability in a case of performing the recording and/or reproducing of data at different head tilt angles in the high temperature and low humidity environment.

In the following, the running stability in a case of performing the recording and/or reproducing of data by changing the head tilt angle during the running of the magnetic tape in the high temperature and low humidity environment is also simply referred to as “running stability”. In addition, the high temperature and low humidity environment can be, for example, an environment having a temperature of approximately 30° C. to 50° C. A humidity of the environment can be, for example, approximately 0% to 30% as a relative humidity. The temperatures and the humidity described for the environment in the specification are an atmosphere temperature and a relative humidity of such an environment.

Edge Portion Ra, Central Portion Ra, Ra Ratio (Central Portion Ra/Edge Portion Ra)

In the present invention and the present specification, the arithmetic average roughness Ra is measured by a noncontact optical surface roughness meter. The measurement conditions and data processing conditions are as follows. As the noncontact optical surface roughness meter, for example, Bruker's noncontact optical surface roughness meter Contour can be used, and in examples which will be described later, this noncontact optical surface roughness meter was used.

Measurement Conditions

Measurement environment: Temperature of 23° C. and relative humidity of 50%

Measurement mode: Phase Shift Interferometry (PSI)

Objective lens: 10×

Intermediate lens: 1.0×

Visual field for measurement: 355 μm×474 μm

Data Processing Conditions

Distortion/tilt correction: Cylinder and Tilt (Zero Level: Zero Mean)

Filter: Gaussian

-   -   Band Pass: Order=0     -   Type=Regular     -   High Pass Filter=1.11 μm     -   Low Pass Filter=50 μm

In the present invention and the present specification, the edge portion Ra which is the arithmetic average roughness Ra measured at the edge portion of the surface of the magnetic layer is a value obtained by the following method.

Both ends of the magnetic tape in the width direction are called edges.

At an arbitrary position on the surface of the magnetic layer of the magnetic tape to be measured, one edge is included in the visual field for measurement, and measurement is performed with the noncontact optical surface roughness meter under the measurement conditions described above.

After data processing is performed on the obtained measurement results under the data processing conditions described above, a range of 200 μm in width×200 μm in length (that is, distance of the magnetic tape in the longitudinal direction) is designated at an arbitrary position in the visual field for measurement, in a region having a width of 200 μm from a “position of an inner side of 50 μm from the edge” to a “position of an inner side of 200 μm further from the position of the inner side of 50 μm from the edge”, and the Ra of the designated range is obtained. An analysis unit provided in the noncontact optical surface roughness meter can calculate and output the Ra.

Then, the other edge is included in the visual field for measurement and the Ra is obtained by the method described above.

For each of the one edge side and the other edge side, the measurement is performed three times in total by shifting the measurement position by 1 mm or more.

By the measurement described above, a total of 6 Ras are obtained. The arithmetic average of the Ras obtained accordingly is defined as the edge portion Ra.

In the present invention and the present specification, the central portion Ra which is the arithmetic average roughness Ra measured at the central portion of the surface of the magnetic layer is a value obtained by the following method.

On the surface of the magnetic layer, for one edge randomly selected from both edges of the magnetic tape, a range of 200 μm in width×200 μm in length is designated at an arbitrary position in the visual field for measurement, in a region having a width of 6 mm from a “position of an inner side of 3 mm from the edge” to a “position of an inner side of 6 mm further from the position of the inner side of 3 mm from the edge”, and the Ra of the designated range is obtained. For the edge side selected above, the measurement is performed six times in total by shifting the measurement position by 1 mm or more.

By the measurement described above, a total of 6 Ras are obtained. The arithmetic average of the Ras obtained accordingly is defined as the central portion Ra.

The Ra ratio (central portion Ra/edge portion Ra) is calculated from the edge portion Ra and the central portion Ra obtained by the method described above. In the magnetic tape described above, the Ra ratio (central portion Ra/edge portion Ra) is 0.75 or more, preferably 0.77 or more, and more preferably 0.80 or more, from a viewpoint of improving the running stability in a case of performing the recording and/or reproducing of data at different head tilt angles in the high temperature and low humidity environment. In addition, from the viewpoint described above, the Ra ratio (central portion Ra/edge portion Ra) is 0.95 or less, preferably 0.93 or less, and more preferably 0.90 or less.

In the magnetic tape described above, the edge portion Ra is 1.50 nm or less, preferably 1.30 nm or less, more preferably 1.00 nm or less, even more preferably 0.95 nm or less, and still preferably 0.90 nm or less, from a viewpoint of improving the running stability. The edge portion Ra can be, for example, 0.10 nm or more, 0.20 nm or more, or 0.30 nm or more, or can be less than the value exemplified here.

In the magnetic tape, the central portion Ra is 1.30 nm or less, preferably 1.20 nm or less, more preferably 1.10 nm or less, even more preferably 1.00 nm or less, still preferably 0.90 nm or less, and still more preferably 0.80 nm or less, from a viewpoint of improving the running stability. In addition, from the viewpoint described above, the central portion Ra is 0.30 nm or more, preferably 0.40 nm or more, and more preferably 0.50 nm or more.

A control method of the Ra ratio, the edge portion Ra, and the central portion Ra will be described later.

Standard Deviation of Curvature

Next, a standard deviation of a curvature will be described.

The curvature of the magnetic tape in the longitudinal direction of the present invention and the present specification is a value obtained by the following method in an environment of an atmosphere temperature of 23° C. and a relative humidity of 50%. The magnetic tape is normally accommodated and circulated in a magnetic tape cartridge. As the magnetic tape to be measured, a magnetic tape taken out from an unused magnetic tape cartridge that is not attached to the magnetic tape device is used.

FIG. 4 is an explanatory diagram of the curvature of the magnetic tape in the longitudinal direction.

A tape sample having a length of 100 m in the longitudinal direction is cut out from a randomly selected portion of the magnetic tape to be measured. One end of this tape sample is defined as a position of 0 m, and a position spaced apart from this one end toward the other end by D m (D meters) in the longitudinal direction is defined as a position of D m. Accordingly, a position spaced apart by 10 m in the longitudinal direction is defined as a position of 10 m, a position spaced apart by 20 m is defined as a position of 20 m, and in this manner, a position of 30 m, a position of 40 m, a position of 50 m, a position of 60 m, a position of 70 m, a position of 80 m, a position of 90 m, and a position of 100 m are defined at intervals of 10 m sequentially.

A tape sample having a length of 1 m from the 0 m position to the position of 1 m is cut out. This tape sample is used as a tape sample for measuring the curvature at the position of 0 m.

A tape sample having a length of 1 m from the 10 m position to the position of 11 m is cut out. This tape sample is used as a tape sample for measuring the curvature at the position of 10 m.

A tape sample having a length of 1 m from the 20 m position to the position of 21 m is cut out. This tape sample is used as a tape sample for measuring the curvature at the position of 20 m.

A tape sample having a length of 1 m from the 30 m position to the position of 31 m is cut out. This tape sample is used as a tape sample for measuring the curvature at the position of 30 m.

A tape sample having a length of 1 m from the 40 m position to the position of 41 m is cut out. This tape sample is used as a tape sample for measuring the curvature at the position of 40 m.

A tape sample having a length of 1 m from the 50 m position to the position of 51 m is cut out. This tape sample is used as a tape sample for measuring the curvature at the position of 50 m.

A tape sample having a length of 1 m from the 60 m position to the position of 61 m is cut out. This tape sample is used as a tape sample for measuring the curvature at the position of 60 m.

A tape sample having a length of 1 m from the 70 m position to the position of 71 m is cut out. This tape sample is used as a tape sample for measuring the curvature at the position of 70 m.

A tape sample having a length of 1 m from the 80 m position to the position of 81 m is cut out. This tape sample is used as a tape sample for measuring the curvature at the position of 80 m.

A tape sample having a length of 1 m from the 90 m position to the position of 91 m is cut out. This tape sample is used as a tape sample for measuring the curvature at the position of 90 m.

A tape sample having a length of 1 m from the 99 m position to the position of 100 m is cut out. This tape sample is used as a tape sample for measuring the curvature at the position of 100 m.

The tape sample of each position is hung for 24 hours±4 hours in a tension-free state by gripping an upper end portion with a gripping member (clip or the like) by setting the longitudinal direction as the vertical direction. Then, within 1 hour, the following measurement is performed.

As shown in FIG. 4 , the tape piece is placed on a flat surface in a tension-free state. The tape piece may be placed on a flat surface with the surface on the magnetic layer side facing upward, or may be placed on a flat surface with the other surface facing upward. In FIG. 4 , S indicates a tape sample and W indicates the width direction of the tape sample. Using an optical microscope, a distance L1 (unit: mm) that is a shortest distance between a virtual line 54 connecting both terminal portions 52 and 53 of the tape sample S and a maximum curved portion 55 in the longitudinal direction of the tape sample S is measured. FIG. 4 shows an example in which the tape sample is curved upward on a paper surface. Even in a case where the tape sample is curved downward, the distance L1 (mm) is measured in the same manner. The distance L1 is displayed as a positive value regardless of which side is curved. In a case where no curve in the longitudinal direction is confirmed, the L1 is set to 0 (zero) mm.

By doing so, a standard deviation of the curvature L1 measured for a total of 11 positions from the position of 0 m to the position of 100 m (that is, a positive square root of the dispersion) is the standard deviation of the curvature of the magnetic tape to be measured in the longitudinal direction (unit: mm/m).

In the magnetic tape, the standard deviation of the curvature obtained by the method described above can be, for example, 7 mm/m or less and 6 mm/m or less, and from a viewpoint of further improving the running stability, it is preferably 5 mm/m or less, more preferably 4 mm/m or less, and even more preferably 3 mm/m or less. The standard deviation of the curvature of the magnetic tape can be, for example, 0 mm/m or more, more than 0 mm/m, 1 mm/m or more, or 2 mm/m or more. It is preferable that the value of the standard deviation of the curvature is small, from a viewpoint of further improving the running stability.

The standard deviation of the curvature can be controlled by adjusting the manufacturing conditions of the manufacturing step of the magnetic tape. This point will be described later in detail.

Hereinafter, the magnetic tape will be described more specifically.

Magnetic Layer

Ferromagnetic Powder

As the ferromagnetic powder contained in the magnetic layer, a well-known ferromagnetic powder can be used as one kind or in combination of two or more kinds as the ferromagnetic powder used in the magnetic layer of various magnetic recording media. It is preferable to use a ferromagnetic powder having an average particle size as the ferromagnetic powder, from a viewpoint of improvement of a recording density. From this viewpoint, an average particle size of the ferromagnetic powder is preferably equal to or smaller than 50 nm, more preferably equal to or smaller than 45 nm, even more preferably equal to or smaller than 40 nm, further preferably equal to or smaller than 35 nm, further more preferably equal to or smaller than 30 nm, further even more preferably equal to or smaller than 25 nm, and still preferably equal to or smaller than 20 nm. Meanwhile, from a viewpoint of stability of magnetization, the average particle size of the ferromagnetic powder is preferably equal to or greater than 5 nm, more preferably equal to or greater than 8 nm, even more preferably equal to or greater than 10 nm, still preferably equal to or greater than 15 nm, and still more preferably equal to or greater than 20 nm.

Hexagonal Ferrite Powder

As a preferred specific example of the ferromagnetic powder, a hexagonal ferrite powder can be used. For details of the hexagonal ferrite powder, descriptions disclosed in paragraphs 0012 to 0030 of JP2011-225417A, paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 of JP2012-204726A, and paragraphs 0029 to 0084 of JP2015-127985A can be referred to, for example.

In the invention and the specification, the “hexagonal ferrite powder” is a ferromagnetic powder in which a hexagonal ferrite type crystal structure is detected as a main phase by X-ray diffraction analysis. The main phase is a structure to which a diffraction peak at the highest intensity in an X-ray diffraction spectrum obtained by the X-ray diffraction analysis belongs. For example, in a case where the diffraction peak at the highest intensity in the X-ray diffraction spectrum obtained by the X-ray diffraction analysis belongs to a hexagonal ferrite type crystal structure, it is determined that the hexagonal ferrite type crystal structure is detected as a main phase. In a case where only a single structure is detected by the X-ray diffraction analysis, this detected structure is set as a main phase. The hexagonal ferrite type crystal structure includes at least an iron atom, a divalent metal atom, and an oxygen atom as constituting atoms. A divalent metal atom is a metal atom which can be divalent cations as ions, and examples thereof include an alkali earth metal atom such as a strontium atom, a barium atom, or a calcium atom, and a lead atom. In the invention and the specification, the hexagonal strontium ferrite powder is powder in which a main divalent metal atom included in this powder is a strontium atom, and the hexagonal barium ferrite powder is a powder in which a main divalent metal atom included in this powder is a barium atom. The main divalent metal atom is a divalent metal atom occupying the greatest content in the divalent metal atom included in the powder based on atom %. However, the divalent metal atom described above does not include rare earth atom. The “rare earth atom” of the invention and the specification is selected from the group consisting of a scandium atom (Sc), an yttrium atom (Y), and a lanthanoid atom. The lanthanoid atom is selected from the group consisting of a lanthanum atom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymium atom (Nd), a promethium atom (Pm), a samarium atom (Sm), an europium atom (Eu), a gadolinium atom (Gd), a terbium atom (Tb), a dysprosium atom (Dy), a holmium atom (Ho), an erbium atom (Er), a thulium atom (Tm), an ytterbium atom (Yb), and a lutetium atom (Lu).

Hereinafter, the hexagonal strontium ferrite powder which is one aspect of the hexagonal ferrite powder will be described more specifically.

An activation volume of the hexagonal strontium ferrite powder is preferably in a range of 800 to 1,600 nm³. The atomized hexagonal strontium ferrite powder showing the activation volume in the range described above is suitable for manufacturing a magnetic tape exhibiting excellent electromagnetic conversion characteristics. The activation volume of the hexagonal strontium ferrite powder is preferably equal to or greater than 800 nm³, and can also be, for example, equal to or greater than 850 nm³. In addition, from a viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the hexagonal strontium ferrite powder is more preferably equal to or smaller than 1,500 nm³, even more preferably equal to or smaller than 1,400 nm³, still preferably equal to or smaller than 1,300 nm³, still more preferably equal to or smaller than 1,200 nm³, and still even more preferably equal to or smaller than 1,100 nm³. The same applies to the activation volume of the hexagonal barium ferrite powder.

The “activation volume” is a unit of magnetization reversal and an index showing a magnetic magnitude of the particles. Regarding the activation volume and an anisotropy constant Ku which will be described later disclosed in the invention and the specification, magnetic field sweep rates of a coercivity Hc measurement part at time points of 3 minutes and 30 minutes are measured by using an oscillation sample type magnetic-flux meter (measurement temperature: 23° C.±1° C.), and the activation volume and the anisotropy constant Ku are values acquired from the following relational expression of Hc and an activation volume V. A unit of the anisotropy constant Ku is 1 erg/cc=1.0×10⁻¹ J/m³. Hc=2Ku/Ms{1−[(kT/KuV)ln(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant (unit: J/m³), Ms: saturation magnetization (unit: kA/m), k: Boltzmann's constant, T: absolute temperature (unit: K), V: activation volume (unit: cm³), A: spin precession frequency (unit: s⁻¹), and t: magnetic field reversal time (unit: s)]

The anisotropy constant Ku can be used as an index of reduction of thermal fluctuation, that is, improvement of thermal stability. The hexagonal strontium ferrite powder can preferably have Ku equal to or greater than 1.8×10⁵ J/m³, and more preferably have Ku equal to or greater than 2.0×10⁵ J/m³. In addition, Ku of the hexagonal strontium ferrite powder can be, for example, equal to or smaller than 2.5×10⁵ J/m³. However, the high Ku is preferable, because it means high thermal stability, and thus, Ku is not limited to the exemplified value.

The hexagonal strontium ferrite powder may or may not include the rare earth atom. In a case where the hexagonal strontium ferrite powder includes the rare earth atom, a content (bulk content) of the rare earth atom is preferably 0.5 to 5.0 atom % with respect to 100 atom % of the iron atom. In one embodiment, the hexagonal strontium ferrite powder including the rare earth atom can have a rare earth atom surface layer portion uneven distribution. The “rare earth atom surface layer portion uneven distribution” of the invention and the specification means that a content of rare earth atom with respect to 100 atom % of iron atom in a solution obtained by partially dissolving the hexagonal strontium ferrite powder with acid (hereinafter, referred to as a “rare earth atom surface layer portion content” or simply a “surface layer portion content” regarding the rare earth atom) and a content of rare earth atom with respect to 100 atom % of iron atom in a solution obtained by totally dissolving the hexagonal strontium ferrite powder with acid (hereinafter, referred to as a “rare earth atom bulk content” or simply a “bulk content” regarding the rare earth atom) satisfy a ratio of rare earth atom surface layer portion content/rare earth atom bulk content >1.0.

The content of rare earth atom of the hexagonal strontium ferrite powder which will be described later is identical to the rare earth atom bulk content. With respect to this, the partial dissolving using acid is to dissolve the surface layer portion of particles configuring the hexagonal strontium ferrite powder, and accordingly, the content of rare earth atom in the solution obtained by the partial dissolving is the content of rare earth atom in the surface layer portion of the particles configuring the hexagonal strontium ferrite powder. The rare earth atom surface layer portion content satisfying a ratio of “rare earth atom surface layer portion content/rare earth atom bulk content >1.0” means that the rare earth atoms are unevenly distributed in the surface layer portion (that is, a larger amount of the rare earth atoms is present, compared to that inside), among the particles configuring the hexagonal strontium ferrite powder. The surface layer portion of the invention and the specification means a part of the region of the particles configuring the hexagonal strontium ferrite powder towards the inside from the surface.

In a case where the hexagonal strontium ferrite powder includes the rare earth atom, a content (bulk content) of the rare earth atom is preferably in a range of 0.5 to 5.0 atom % with respect to 100 atom % of the iron atom. It is thought that the rare earth atom having the bulk content in the range described above and uneven distribution of the rare earth atom in the surface layer portion of the particles configuring the hexagonal strontium ferrite powder contribute to the prevention of a decrease in reproducing output during the repeated reproducing. It is surmised that this is because the rare earth atom having the bulk content in the range described above included in the hexagonal strontium ferrite powder and the uneven distribution of the rare earth atom in the surface layer portion of the particles configuring the hexagonal strontium ferrite powder can increase the anisotropy constant Ku. As the value of the anisotropy constant Ku is high, occurrence of a phenomenon called thermal fluctuation (that is, improvement of thermal stability) can be prevented. By preventing the occurrence of the thermal fluctuation, a decrease in reproducing output during the repeated reproducing can be prevented. It is surmised that the uneven distribution of the rare earth atom in the surface layer portion of the particles of the hexagonal strontium ferrite powder contributes to stabilization of a spin at an iron (Fe) site in a crystal lattice of the surface layer portion, thereby increasing the anisotropy constant Ku.

In addition, it is surmised that the use of the hexagonal strontium ferrite powder having the rare earth atom surface layer portion uneven distribution as the ferromagnetic powder of the magnetic layer also contributes to the prevention of chipping of the surface of the magnetic layer due to the sliding with the magnetic head. That is, it is surmised that, the hexagonal strontium ferrite powder having the rare earth atom surface layer portion uneven distribution can also contribute to the improvement of running durability of the magnetic tape. It is surmised that this is because the uneven distribution of the rare earth atom on the surface of the particles configuring the hexagonal strontium ferrite powder contributes to improvement of an interaction between the surface of the particles and an organic substance (for example, binding agent and/or additive) included in the magnetic layer, thereby improving hardness of the magnetic layer.

From a viewpoint of preventing reduction of the reproduction output in the repeated reproduction and/or a viewpoint of further improving running durability, the content of rare earth atom (bulk content) is more preferably in a range of 0.5 to 4.5 atom %, even more preferably in a range of 1.0 to 4.5 atom %, and still preferably in a range of 1.5 to 4.5 atom %.

The bulk content is a content obtained by totally dissolving the hexagonal strontium ferrite powder. In the invention and the specification, the content of the atom is a bulk content obtained by totally dissolving the hexagonal strontium ferrite powder, unless otherwise noted. The hexagonal strontium ferrite powder including the rare earth atom may include only one kind of rare earth atom or may include two or more kinds of rare earth atom, as the rare earth atom. In a case where two or more kinds of rare earth atoms are included, the bulk content is obtained from the total of the two or more kinds of rare earth atoms. The same also applies to the other components of the invention and the specification. That is, for a given component, only one kind may be used or two or more kinds may be used, unless otherwise noted. In a case where two or more kinds are used, the content is a content of the total of the two or more kinds.

In a case where the hexagonal strontium ferrite powder includes the rare earth atom, the rare earth atom included therein may be any one or more kinds of the rare earth atom. Examples of the rare earth atom preferable from a viewpoint of preventing reduction of the reproduction output during the repeated reproduction include a neodymium atom, a samarium atom, an yttrium atom, and a dysprosium atom, a neodymium atom, a samarium atom, an yttrium atom are more preferable, and a neodymium atom is even more preferable.

In the hexagonal strontium ferrite powder having the rare earth atom surface layer portion uneven distribution, a degree of uneven distribution of the rare earth atom is not limited, as long as the rare earth atom is unevenly distributed in the surface layer portion of the particles configuring the hexagonal strontium ferrite powder. For example, regarding the hexagonal strontium ferrite powder having the rare earth atom surface layer portion uneven distribution, a ratio of the surface layer portion content of the rare earth atom obtained by partial dissolving performed under the dissolving conditions which will be described later and the bulk content of the rare earth atom obtained by total dissolving performed under the dissolving conditions which will be described later, “surface layer portion content/bulk content” is greater than 1.0 and can be equal to or greater than 1.5. The “surface layer portion content/bulk content” greater than 1.0 means that the rare earth atoms are unevenly distributed in the surface layer portion (that is, a larger amount of the rare earth atoms is present, compared to that inside), in the particles configuring the hexagonal strontium ferrite powder. A ratio of the surface layer portion content of the rare earth atom obtained by partial dissolving performed under the dissolving conditions which will be described later and the bulk content of the rare earth atom obtained by total dissolving performed under the dissolving conditions which will be described later, “surface layer portion content/bulk content” can be, for example, equal to or smaller than 10.0, equal to or smaller than 9.0, equal to or smaller than 8.0, equal to or smaller than 7.0, equal to or smaller than 6.0, equal to or smaller than 5.0, or equal to or smaller than 4.0. However, in the hexagonal strontium ferrite powder having the rare earth atom surface layer portion uneven distribution, the “surface layer portion content/bulk content” is not limited to the exemplified upper limit or the lower limit, as long as the rare earth atom is unevenly distributed in the surface layer portion of the particles configuring the hexagonal strontium ferrite powder.

The partial dissolving and the total dissolving of the hexagonal strontium ferrite powder will be described below. Regarding the hexagonal strontium ferrite powder present as the powder, sample powder for the partial dissolving and the total dissolving are collected from powder of the same batch. Meanwhile, regarding the hexagonal strontium ferrite powder included in a magnetic layer of a magnetic tape, a part of the hexagonal strontium ferrite powder extracted from the magnetic layer is subjected to the partial dissolving and the other part is subjected to the total dissolving. The extraction of the hexagonal strontium ferrite powder from the magnetic layer can be performed by, for example, a method disclosed in a paragraph 0032 of JP2015-91747A.

The partial dissolving means dissolving performed so that the hexagonal strontium ferrite powder remaining in the solution can be visually confirmed in a case of the completion of the dissolving. For example, by performing the partial dissolving, a region of the particles configuring the hexagonal strontium ferrite powder which is 10% to 20% by mass with respect to 100% by mass of a total of the particles can be dissolved. On the other hand, the total dissolving means dissolving performed until the hexagonal strontium ferrite powder remaining in the solution is not visually confirmed in a case of the completion of the dissolving.

The partial dissolving and the measurement of the surface layer portion content are, for example, performed by the following method. However, dissolving conditions such as the amount of sample powder and the like described below are merely examples, and dissolving conditions capable of performing the partial dissolving and the total dissolving can be randomly used.

A vessel (for example, beaker) containing 12 mg of sample powder and 10 mL of hydrochloric acid having a concentration of 1 mol/L is held on a hot plate at a set temperature of 70° C. for 1 hour. The obtained solution is filtered with a membrane filter having a hole diameter of 0.1 μm. The element analysis of the filtrate obtained as described above is performed by an inductively coupled plasma (ICP) analysis device. By doing so, the surface layer portion content of the rare earth atom with respect to 100 atom % of the iron atom can be obtained. In a case where a plurality of kinds of rare earth atoms are detected from the element analysis, a total content of the entirety of the rare earth atoms is the surface layer portion content. The same applies to the measurement of the bulk content.

Meanwhile, the total dissolving and the measurement of the bulk content are, for example, performed by the following method.

A vessel (for example, beaker) containing 12 mg of sample powder and 10 mL of hydrochloric acid having a concentration of 4 mol/L is held on a hot plate at a set temperature of 80° C. for 3 hours. After that, the process is performed in the same manner as in the partial dissolving and the measurement of the surface layer portion content, and the bulk content with respect to 100 atom % of the iron atom can be obtained.

From a viewpoint of increasing reproducing output in a case of reproducing data recorded on a magnetic tape, it is desirable that the mass magnetization σs of ferromagnetic powder contained in the magnetic tape is high. In regards to this point, in hexagonal strontium ferrite powder which includes the rare earth atom but does not have the rare earth atom surface layer portion uneven distribution, σs tends to significantly decrease, compared to that in hexagonal strontium ferrite powder not including the rare earth atom. With respect to this, it is thought that, hexagonal strontium ferrite powder having the rare earth atom surface layer portion uneven distribution is also preferable for preventing such a significant decrease in σs. In one embodiment, σs of the hexagonal strontium ferrite powder can be equal to or greater than 45 A×m²/kg and can also be equal to or greater than 47 A×m²/kg. On the other hand, from a viewpoint of noise reduction, σs is preferably equal to or smaller than 80 A×m²/kg and more preferably equal to or smaller than 60 A×m²/kg. σs can be measured by using a well-known measurement device capable of measuring magnetic properties such as an oscillation sample type magnetic-flux meter. In the invention and the specification, the mass magnetization σs is a value measured at a magnetic field strength of 15 kOe, unless otherwise noted. 1 [kOe]=(10⁶/4π) [A/m]

Regarding the content (bulk content) of the constituting atom in the hexagonal strontium ferrite powder, a content of the strontium atom can be, for example, in a range of 2.0 to 15.0 atom % with respect to 100 atom % of the iron atom. In one embodiment, in the hexagonal strontium ferrite powder, the divalent metal atom included in this powder can be only a strontium atom. In another embodiment, the hexagonal strontium ferrite powder can also include one or more kinds of other divalent metal atoms, in addition to the strontium atom. For example, the hexagonal strontium ferrite powder can include a barium atom and/or a calcium atom. In a case where the other divalent metal atom other than the strontium atom is included, a content of a barium atom and a content of a calcium atom in the hexagonal strontium ferrite powder respectively can be, for example, in a range of 0.05 to 5.0 atom % with respect to 100 atom % of the iron atom.

As the crystal structure of the hexagonal ferrite, a magnetoplumbite type (also referred to as an “M type”), a W type, a Y type, and a Z type are known. The hexagonal strontium ferrite powder may have any crystal structure. The crystal structure can be confirmed by X-ray diffraction analysis. In the hexagonal strontium ferrite powder, a single crystal structure or two or more kinds of crystal structure can be detected by the X-ray diffraction analysis. For example, In one embodiment, in the hexagonal strontium ferrite powder, only the M type crystal structure can be detected by the X-ray diffraction analysis. For example, the M type hexagonal ferrite is represented by a compositional formula of AFe₁₂O₁₉. Here, A represents a divalent metal atom, in a case where the hexagonal strontium ferrite powder has the M type, A is only a strontium atom (Sr), or in a case where a plurality of divalent metal atoms are included as A, the strontium atom (Sr) occupies the hexagonal strontium ferrite powder with the greatest content based on atom % as described above. A content of the divalent metal atom in the hexagonal strontium ferrite powder is generally determined according to the type of the crystal structure of the hexagonal ferrite and is not particularly limited. The same applies to a content of an iron atom and a content of an oxygen atom. The hexagonal strontium ferrite powder at least includes an iron atom, a strontium atom, and an oxygen atom, and can also include a rare earth atom. In addition, the hexagonal strontium ferrite powder may or may not include atoms other than these atoms. As an example, the hexagonal strontium ferrite powder may include an aluminum atom (Al). A content of the aluminum atom can be, for example, 0.5 to 10.0 atom % with respect to 100 atom % of the iron atom. From a viewpoint of preventing the reduction of the reproduction output during the repeated reproduction, the hexagonal strontium ferrite powder includes the iron atom, the strontium atom, the oxygen atom, and the rare earth atom, and a content of the atoms other than these atoms is preferably equal to or smaller than 10.0 atom %, more preferably in a range of 0 to 5.0 atom %, and may be 0 atom % with respect to 100 atom % of the iron atom. That is, In one embodiment, the hexagonal strontium ferrite powder may not include atoms other than the iron atom, the strontium atom, the oxygen atom, and the rare earth atom. The content shown with atom % described above is obtained by converting a value of the content (unit: % by mass) of each atom obtained by totally dissolving the hexagonal strontium ferrite powder into a value shown as atom % by using the atomic weight of each atom. In addition, in the invention and the specification, a given atom which is “not included” means that the content thereof obtained by performing total dissolving and measurement by using an ICP analysis device is 0% by mass. A detection limit of the ICP analysis device is generally equal to or smaller than 0.01 ppm (parts per million) based on mass. The expression “not included” is used as a meaning including that a given atom is included with the amount smaller than the detection limit of the ICP analysis device. In one embodiment, the hexagonal strontium ferrite powder does not include a bismuth atom (Bi).

Metal Powder

As a preferred specific example of the ferromagnetic powder, a ferromagnetic metal powder can also be used. For details of the ferromagnetic metal powder, descriptions disclosed in paragraphs 0137 to 0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A can be referred to, for example.

ε-Iron Oxide Powder

As a preferred specific example of the ferromagnetic powder, an ε-iron oxide powder can also be used. In the invention and the specification, the “ε-iron oxide powder” is a ferromagnetic powder in which an ε-iron oxide type crystal structure is detected as a main phase by X-ray diffraction analysis. For example, in a case where the diffraction peak at the highest intensity in the X-ray diffraction spectrum obtained by the X-ray diffraction analysis belongs to an ε-iron oxide type crystal structure, it is determined that the ε-iron oxide type crystal structure is detected as a main phase. As a manufacturing method of the ε-iron oxide powder, a manufacturing method from a goethite, a reverse micelle method, and the like are known. All of the manufacturing methods are well known. For the method of manufacturing the ε-iron oxide powder in which a part of Fe is substituted with substitutional atoms such as Ga, Co, Ti, Al, or Rh, a description disclosed in J. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. 51, pp. S280-S284, J. Mater. Chem. C, 2013, 1, pp. 5200-5206 can be referred, for example. However, the manufacturing method of the ε-iron oxide powder capable of being used as the ferromagnetic powder in the magnetic layer of the magnetic tape is not limited to the method described here.

An activation volume of the ε-iron oxide powder is preferably in a range of 300 to 1,500 nm³. The atomized ε-iron oxide powder showing the activation volume in the range described above is suitable for manufacturing a magnetic tape exhibiting excellent electromagnetic conversion characteristics. The activation volume of the ε-iron oxide powder is preferably equal to or greater than 300 nm³, and can also be, for example, equal to or greater than 500 nm³. In addition, from a viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the ε-iron oxide powder is more preferably equal to or smaller than 1,400 nm³, even more preferably equal to or smaller than 1,300 nm³, still preferably equal to or smaller than 1,200 nm³, and still more preferably equal to or smaller than 1,100 nm³.

The anisotropy constant Ku can be used as an index of reduction of thermal fluctuation, that is, improvement of thermal stability. The ε-iron oxide powder can preferably have Ku equal to or greater than 3.0×10⁴ J/m³, and more preferably have Ku equal to or greater than 8.0×10⁴ J/m³. In addition, Ku of the ε-iron oxide powder can be, for example, equal to or smaller than 3.0×10⁵ J/m³. However, the high Ku is preferable, because it means high thermal stability, and thus, Ku is not limited to the exemplified value.

From a viewpoint of increasing reproducing output in a case of reproducing data recorded on a magnetic tape, it is desirable that the mass magnetization σs of ferromagnetic powder contained in the magnetic tape is high. In regard to this point, in one embodiment, σs of the ε-iron oxide powder can be equal to or greater than 8 A×m²/kg and can also be equal to or greater than 12 A×m²/kg. On the other hand, from a viewpoint of noise reduction, σs of the ε-iron oxide powder is preferably equal to or smaller than 40 A×m²/kg and more preferably equal to or smaller than 35 A×m²/kg.

In the invention and the specification, average particle sizes of various powder such as the ferromagnetic powder and the like are values measured by the following method with a transmission electron microscope, unless otherwise noted.

The powder is imaged at an imaging magnification ratio of 100,000 with a transmission electron microscope, the image is printed on photographic printing paper or displayed on a display so that the total magnification ratio of 500,000 to obtain an image of particles configuring the powder. A target particle is selected from the obtained image of particles, an outline of the particle is traced with a digitizer, and a size of the particle (primary particle) is measured. The primary particle is an independent particle which is not aggregated.

The measurement described above is performed regarding 500 particles arbitrarily extracted. An arithmetic average of the particle size of 500 particles obtained as described above is the average particle size of the powder. As the transmission electron microscope, a transmission electron microscope H-9000 manufactured by Hitachi, Ltd. can be used, for example. In addition, the measurement of the particle size can be performed by a well-known image analysis software, for example, image analysis software KS-400 manufactured by Carl Zeiss. The average particle size shown in examples which will be described later is a value measured by using transmission electron microscope H-9000 manufactured by Hitachi, Ltd. as the transmission electron microscope, and image analysis software KS-400 manufactured by Carl Zeiss as the image analysis software, unless otherwise noted. In the invention and the specification, the powder means an aggregate of a plurality of particles. For example, the ferromagnetic powder means an aggregate of a plurality of ferromagnetic particles. The aggregate of the plurality of particles not only includes an embodiment in which particles configuring the aggregate are directly in contact with each other, but also includes an embodiment in which a binding agent or an additive which will be described later is interposed between the particles. A term, particles may be used for representing the powder.

As a method for collecting a sample powder from the magnetic tape in order to measure the particle size, a method disclosed in a paragraph of 0015 of JP2011-048878A can be used, for example.

In the invention and the specification, unless otherwise noted,

-   -   (1) in a case where the shape of the particle observed in the         particle image described above is a needle shape, a fusiform         shape, or a columnar shape (here, a height is greater than a         maximum long diameter of a bottom surface), the size (particle         size) of the particles configuring the powder is shown as a         length of a major axis configuring the particle, that is, a         major axis length,     -   (2) in a case where the shape of the particle is a planar shape         or a columnar shape (here, a thickness or a height is smaller         than a maximum long diameter of a plate surface or a bottom         surface), the particle size is shown as a maximum long diameter         of the plate surface or the bottom surface, and     -   (3) in a case where the shape of the particle is a sphere shape,         a polyhedron shape, or an unspecified shape, and the major axis         configuring the particles cannot be specified from the shape,         the particle size is shown as an equivalent circle diameter. The         equivalent circle diameter is a value obtained by a circle         projection method.

In addition, regarding an average acicular ratio of the powder, a length of a minor axis, that is, a minor axis length of the particles is measured in the measurement described above, a value of (major axis length/minor axis length) of each particle is obtained, and an arithmetic average of the values obtained regarding 500 particles is calculated. Here, unless otherwise noted, in a case of (1), the minor axis length as the definition of the particle size is a length of a minor axis configuring the particle, in a case of (2), the minor axis length is a thickness or a height, and in a case of (3), the major axis and the minor axis are not distinguished, thus, the value of (major axis length/minor axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of the particle is specified, for example, in a case of definition of the particle size (1), the average particle size is an average major axis length, and in a case of the definition (2), the average particle size is an average plate diameter. In a case of the definition (3), the average particle size is an average diameter (also referred to as an average particle diameter).

The content (filling percentage) of the ferromagnetic powder of the magnetic layer is preferably in a range of 50% to 90% by mass and more preferably in a range of 60% to 90% by mass with respect to a total mass of the magnetic layer. A high filling percentage of the ferromagnetic powder in the magnetic layer is preferable from a viewpoint of improvement of recording density.

Binding Agent

The magnetic tape may be a coating type magnetic tape, and can include a binding agent in the magnetic layer. The binding agent is one or more kinds of resin. As the binding agent, various resins normally used as a binding agent of a coating type magnetic recording medium can be used. As the binding agent, a resin selected from a polyurethane resin, a polyester resin, a polyamide resin, a vinyl chloride resin, an acrylic resin obtained by copolymerizing styrene, acrylonitrile, or methyl methacrylate, a cellulose resin such as nitrocellulose, an epoxy resin, a phenoxy resin, and a polyvinylalkylal resin such as polyvinyl acetal or polyvinyl butyral can be used alone or a plurality of resins can be mixed with each other to be used. Among these, a polyurethane resin, an acrylic resin, a cellulose resin, and a vinyl chloride resin are preferable. These resins may be a homopolymer or a copolymer. These resins can be used as the binding agent even in the non-magnetic layer and/or a back coating layer which will be described later. For the binding agent described above, descriptions disclosed in paragraphs 0028 to 0031 of JP2010-24113A can be referred to. In addition, the binding agent may be a radiation curable resin such as an electron beam curable resin. For the radiation curable resin, paragraphs 0044 and 0045 of JP2011-048878A can be referred to.

An average molecular weight of the resin used as the binding agent can be, for example, 10,000 to 200,000 as a weight-average molecular weight. The weight-average molecular weight of the invention and the specification is a value obtained by performing polystyrene conversion of a value measured by gel permeation chromatography (GPC) under the following measurement conditions. The weight-average molecular weight of the binding agent shown in examples which will be described later is a value obtained by performing polystyrene conversion of a value measured under the following measurement conditions. The amount of the binding agent used can be, for example, 1.0 to 30.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder.

GPC device: HLC-8120 (manufactured by Tosoh Corporation)

Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8 mmID (inner diameter)×30.0 cm)

Eluent: Tetrahydrofuran (THF)

Curing Agent

A curing agent can also be used together with the binding agent. As the curing agent, In one embodiment, a thermosetting compound which is a compound in which a curing reaction (crosslinking reaction) proceeds due to heating can be used, and in another embodiment, a photocurable compound in which a curing reaction (crosslinking reaction) proceeds due to light irradiation can be used. At least a part of the curing agent is included in the magnetic layer in a state of being reacted (crosslinked) with other components such as the binding agent, by proceeding the curing reaction in the manufacturing step of the magnetic tape. The preferred curing agent is a thermosetting compound, and polyisocyanate is suitable. For the details of polyisocyanate, descriptions disclosed in paragraphs 0124 and 0125 of JP2011-216149A can be referred to. The amount of the curing agent can be, for example, 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binding agent in the magnetic layer forming composition, and is preferably 50.0 to 80.0 parts by mass, from a viewpoint of improvement of hardness of each layer such as the magnetic layer.

Additives

The magnetic layer may include one or more kinds of additives, as necessary. As the additives, the curing agent described above is used as an example. In addition, examples of the additive included in the magnetic layer include a non-magnetic powder (for example, inorganic powder, carbon black, or the like), a lubricant, a dispersing agent, a dispersing assistant, a fungicide, an antistatic agent, and an antioxidant. For the lubricant, a description disclosed in paragraphs 0030 to 0033, 0035, and 0036 of JP2016-126817A can be referred to. The lubricant may be included in the non-magnetic layer which will be described later. For the lubricant which can be included in the non-magnetic layer, a description disclosed in paragraphs 0030, 0031, 0034 to 0036 of JP2016-126817A can be referred to. For the dispersing agent, a description disclosed in paragraphs 0061 and 0071 of JP2012-133837A can be referred to. The dispersing agent may be added to a non-magnetic layer forming composition. For the dispersing agent which can be added to the non-magnetic layer forming composition, a description disclosed in paragraph 0061 of JP2012-133837A can be referred to. As the non-magnetic powder which may be contained in the magnetic layer, non-magnetic powder which can function as an abrasive, non-magnetic powder (for example, non-magnetic colloid particles) which can function as a projection formation agent which forms projections suitably protruded from the surface of the magnetic layer, and the like can be used. An average particle size of colloidal silica (silica colloid particles) shown in the examples which will be described later is a value obtained by a method disclosed in a measurement method of an average particle diameter in a paragraph 0015 of JP2011-048878A. As the additives, a commercially available product can be suitably selected according to the desired properties or manufactured by a well-known method, and can be used with any amount. As an example of the additive which can be used for improving dispersibility of the abrasive in the magnetic layer including the abrasive, a dispersing agent disclosed in paragraphs 0012 to 0022 of JP2013-131285A can be used.

The magnetic layer described above can be provided on the surface of the non-magnetic support directly or indirectly through the non-magnetic layer.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape may include a magnetic layer directly on the non-magnetic support or may include a non-magnetic layer containing the non-magnetic powder between the non-magnetic support and the magnetic layer. The non-magnetic powder used for the non-magnetic layer may be a powder of an inorganic substance (inorganic powder) or a powder of an organic substance (organic powder). In addition, carbon black and the like can be used. Examples of the inorganic substance include metal, metal oxide, metal carbonate, metal sulfate, metal nitride, metal carbide, and metal sulfide. The non-magnetic powder can be purchased as a commercially available product or can be manufactured by a well-known method. For details thereof, descriptions disclosed in paragraphs 0146 to 0150 of JP2011-216149A can be referred to. For carbon black capable of being used in the non-magnetic layer, a description disclosed in paragraphs 0040 and 0041 of JP2010-24113A can be referred to. The content (filling percentage) of the non-magnetic powder of the non-magnetic layer is preferably in a range of 50% to 90% by mass and more preferably in a range of 60% to 90% by mass with respect to a total mass of the non-magnetic layer.

In one embodiment, the non-magnetic layer can contain a Fe-based inorganic oxide powder as the non-magnetic powder. In the invention and the specification, the “Fe-based inorganic oxide powder” refers to an inorganic oxide powder containing iron as a constituent element. Specific examples of the Fe-based inorganic oxide powder can include an α-iron oxide powder and a goethite powder. In the invention and the specification, the “α-iron oxide powder” is a non-magnetic powder in which an α-iron oxide type crystal structure is detected as a main phase by X-ray diffraction analysis. The α-iron oxide powder is also generally called hematite or the like.

According to the studies of the present inventors regarding the non-magnetic layer, it is found that the non-magnetic layer containing the Fe-based inorganic oxide powder having an average particle volume of 2.0×10⁻⁶ μm³ tends to have high hardness. The present inventors consider that this point is preferable for stably performing a burnishing process which will be described later. The present inventors surmise that, in a case where the burnishing process is stably performed, the edge portion Ra and the central portion Ra can be easily controlled, and as a result, the Ra ratio can be easily controlled. From this point, the average particle volume of the Fe-based inorganic oxide powder contained in the non-magnetic layer is preferably 2.0×10⁻⁶ μm³ or less, more preferably 1.5×10⁻⁶ μm³ or less, and even more preferably 1.0×10⁻⁶ μm³ or less. The average particle volume can be, for example, 1.0×10⁻⁹ μm³ or more or 1.0×10⁻⁸ μm³ or more, or can be less than the value exemplified here.

In the invention and the specification, the average particle volume is a value obtained by the following method.

In order to observe the Fe-based inorganic oxide powder contained in the non-magnetic layer of the magnetic tape, first, as a sample pretreatment, flaking is performed by a microtome method. The flaking is performed so that a flaky sample capable of observing a cross section of the magnetic tape in the thickness direction is obtained along the longitudinal direction of the magnetic tape. In the examples which will be described later, Leica EM UC6 manufactured by Leica was used as a microtome in order to obtain the average particle volume of the Fe-based inorganic oxide powder.

For the obtained flaky sample, a cross section observation is performed so as to include a range from the non-magnetic support to the magnetic layer, using a transmission electron microscope (TEM) at an acceleration voltage of 300 kV and a to magnetic layer of 200,000 times, and a cross-sectional TEM image is obtained. As the transmission electron microscope, for example, JEM-2100Plus manufactured by JEOL Ltd. can be used. For the examples which will be described later, JEM-2100Plus manufactured by JEOL Ltd. was used as a transmission electron microscope, in order to obtain the average particle volume of the Fe-based inorganic oxide powder.

In the obtained cross-sectional TEM image, 50 particles of Fe-based inorganic oxide powder are specified from the particles contained in the non-magnetic layer by using a micro electron beam diffraction method. Electron beam diffraction by the micro electron beam diffraction method is performed using a transmission electron microscope at an acceleration voltage of 200 kV and a camera length of 50 cm. For the examples which will be described later, JEM-2100Plus manufactured by JEOL Ltd. was used as the transmission electron microscope for the electron beam diffraction by the micro electron beam diffraction method.

Then, using the 50 particles of the Fe-based inorganic oxide powder specified as described above, the average particle volume is obtained as follows.

First, a major axis length (hereinafter referred to as “DL”) and a minor axis length (hereinafter referred to as “DS”) of each particle are measured.

The major axis length DL means a maximum distance among distances between two parallel lines drawn from all angles so as to be in contact with a contour of the particle (so-called maximum feret's diameter).

In a case where a direction of the major axis length defined as described above is called a major axis direction, the minor axis length DS means a maximum length among lengths of the particle in a direction orthogonal to the major axis direction of the particle.

Next, an average major axis length DLave is obtained as an arithmetic average of the major axis lengths DL of the 50 measured particles. ave is an abbreviation for average.

In addition, an average minor axis length DSave is obtained as an arithmetic average of the minor axis lengths DS of the 50 particles.

From the average major axis length DLave and the average minor axis length DSave, an average volume Vave of the particles is obtained by the following equation. Vave=π/6×DSave² ×DLave

In addition, in one embodiment, the non-magnetic layer may contain carbon black as the non-magnetic powder. An average particle size of carbon black can be, for example, 10 nm to 50 nm. According to the studies of the present inventors, it is found that the non-magnetic layer containing carbon black having a pH of 5.0 or less tends to have high hardness. The present inventors consider that this point is preferable for stably performing a burnishing process which will be described later. The present inventors surmise that, in a case where the burnishing process is stably performed, the edge portion Ra and the central portion Ra can be easily controlled, and as a result, the Ra ratio can be easily controlled. From this point, the pH of the carbon black contained in the non-magnetic layer is preferably 5.0 or less, and more preferably 4.0 or less. The pH can be, for example, 1.0 or more, 2.0 or more, or 3.0 or more, or can be less than the value exemplified here.

In the present invention and the present specification, the pH of carbon black is a value measured according to the standard test method ASTM D1512.

The non-magnetic layer preferably contains at least one of the Fe-based inorganic oxide powder having an average particle volume of 2.0×10⁻⁶ μm³ or less and the carbon black having a pH of 5.0 or less, and more preferably contains both of them. A content of Fe-based inorganic oxide powder having an average particle volume of 2.0×10⁻⁶ μm³ or less with respect to 100 parts by mass of the total non-magnetic powder contained in the non-magnetic layer can be 50 parts by mass or more, 60 parts by mass or more, or 70 parts by mass or more, and can be, for example, 90 parts by mass or less. A content of carbon black having a pH of 5.0 or less with respect to 100 parts by mass of the total non-magnetic powder contained in the non-magnetic layer can be 10 parts by mass or more or 20 parts by mass or more, and can be, for example, 50 parts by mass or less, 40 parts by mass or less, or 30 parts by mass or less.

The non-magnetic layer can include a binding agent and can also include additives. In regards to other details of a binding agent or additives of the non-magnetic layer, the well-known technology regarding the non-magnetic layer can be applied. In addition, in regards to the type and the content of the binding agent, and the type and the content of the additive, for example, the well-known technology regarding the magnetic layer can be applied.

The non-magnetic layer of the magnetic tape also includes a substantially non-magnetic layer containing a small amount of ferromagnetic powder as impurities, or intentionally, together with the non-magnetic powder. Here, the substantially non-magnetic layer is a layer having a residual magnetic flux density equal to or smaller than 10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100 Oe), or a layer having a residual magnetic flux density equal to or smaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m (100 Oe). It is preferable that the non-magnetic layer does not have a residual magnetic flux density and coercivity.

Non-Magnetic Support

Next, the non-magnetic support will be described. As the non-magnetic support (hereinafter, also simply referred to as a “support”), well-known components such as polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamide imide, aromatic polyamide subjected to biaxial stretching are used. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferable. Corona discharge, plasma treatment, easy-bonding treatment, or heat treatment may be performed with respect to these supports in advance.

Back Coating Layer

The tape may or may not include a back coating layer including a non-magnetic powder on a surface side of the non-magnetic support opposite to the surface side provided with the magnetic layer. The back coating layer preferably includes any one or both of carbon black and inorganic powder. The back coating layer can include a binding agent and can also include additives. For the details of the non-magnetic powder, the binding agent included in the back coating layer and various additives, a well-known technology regarding the back coating layer can be applied, and a well-known technology regarding the magnetic layer and/or the non-magnetic layer can also be applied. For example, for the back coating layer, descriptions disclosed in paragraphs 0018 to 0020 of JP2006-331625A and page 4, line 65, to page 5, line 38, of U.S. Pat. No. 7,029,774B can be referred to.

Various Thicknesses

Regarding a thickness (total thickness) of the magnetic tape, it has been required to increase recording capacity (increase in capacity) of the magnetic tape along with the enormous increase in amount of information in recent years. As a unit for increasing the capacity, a thickness of the magnetic tape is reduced and a length of the magnetic tape accommodated in one reel of the magnetic tape cartridge is increased. From this point, the thickness (total thickness) of the magnetic tape is preferably 5.6 μm or less, more preferably 5.5 μm or less, even more preferably 5.4 μm or less, still preferably 5.3 μm or less, and still more preferably 5.2 μm or less. In addition, from a viewpoint of ease of handling, the thickness of the magnetic tape is preferably 3.0 μm or more and more preferably 3.5 μm or more.

The thickness (total thickness) of the magnetic tape can be measured by the following method.

Ten tape samples (for example, length of 5 to 10 cm) are cut out from a random portion of the magnetic tape, these tape samples are overlapped, and the thickness is measured. A value which is one tenth of the measured thickness (thickness per one tape sample) is set as the tape thickness. The thickness measurement can be performed using a well-known measurement device capable of performing the thickness measurement at 0.1 μm order.

A thickness of the non-magnetic support is preferably 3.0 to 5.0 μm.

A thickness of the magnetic layer can be optimized according to a saturation magnetization amount of a magnetic head used, a head gap length, a recording signal band, and the like, is normally 0.01 μm to 0.15 μm, and is preferably 0.02 μm to 0.12 μm and more preferably 0.03 μm to 0.1 μm, from a viewpoint of realization of high-density recording. The magnetic layer may be at least single layer, the magnetic layer may be separated into two or more layers having different magnetic properties, and a configuration of a well-known multilayered magnetic layer can be applied. A thickness of the magnetic layer in a case where the magnetic layer is separated into two or more layers is the total thickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm and is preferably 0.1 to 1.0 μm.

A thickness of the back coating layer is preferably equal to or smaller than 0.9 μm and more preferably 0.1 to 0.7 μm.

Various thicknesses such as the thickness of the magnetic layer and the like can be obtained by the following method.

A cross section of the magnetic tape in the thickness direction is exposed with an ion beam and the cross section observation of the exposed cross section is performed using a scanning electron microscope or a transmission electron microscope. Various thicknesses can be obtained as the arithmetic average of the thicknesses obtained at two random portions in the cross section observation. Alternatively, various thicknesses can be obtained as a designed thickness calculated under the manufacturing conditions.

Manufacturing Method

Preparation of Each Layer Forming Composition

A step of preparing a composition for forming the magnetic layer, the non-magnetic layer or the back coating layer can generally include at least a kneading step, a dispersing step, and a mixing step provided before and after these steps, in a case where necessary. Each step may be divided into two or more stages. The component used in the preparation of each layer forming composition may be added at an initial stage or in a middle stage of each step. As the solvent, one kind or two or more kinds of various kinds of solvents usually used for producing a coating type magnetic recording medium can be used. For the solvent, a description disclosed in a paragraph 0153 of JP2011-216149A can be referred to, for example. In addition, each component may be separately added in two or more steps. For example, a binding agent may be separately added in a kneading step, a dispersing step, and a mixing step for adjusting viscosity after the dispersion. In order to manufacture the magnetic tape, a well-known manufacturing technology can be used in various steps. In the kneading step, an open kneader, a continuous kneader, a pressure kneader, or a kneader having a strong kneading force such as an extruder is preferably used. For details of the kneading processes, descriptions disclosed in JP1989-106338A (JP-H01-106338A) and JP1989-79274A (JP-H01-79274A) can be referred to. As a disperser, a well-known dispersion device can be used. The filtering may be performed by a well-known method in any stage for preparing each layer forming composition. The filtering can be performed by using a filter, for example. As the filter used in the filtering, a filter having a hole diameter of 0.01 to 3 μm (for example, filter made of glass fiber or filter made of polypropylene) can be used, for example.

Coating Step

The magnetic layer can be formed, for example, by directly applying the magnetic layer forming composition onto the non-magnetic support or performing multilayer coating of the magnetic layer forming composition with the non-magnetic layer forming composition in order or at the same time. In an case of performing an alignment process, while the coating layer of the magnetic layer forming composition is wet, the alignment process is performed with respect to the coating layer in an alignment zone. For the alignment process, various technologies disclosed in a paragraph 0052 of JP2010-24113A can be applied. For example, a homeotropic alignment process can be performed by a well-known method such as a method using a different polar facing magnet. In the alignment zone, a drying speed of the coating layer can be controlled by a temperature and an air flow of the dry air and/or a transporting rate in the alignment zone. In addition, the coating layer may be preliminarily dried before transporting to the alignment zone.

The back coating layer can be formed by applying a back coating layer forming composition onto a side of the non-magnetic support opposite to the side provided with the magnetic layer (or to be provided with the magnetic layer).

For details of the coating for forming each layer, a description disclosed in a paragraph 0066 of JP2010-231843A can be referred to.

Other Steps

After performing the coating step described above, a calendar process can usually be performed in order to improve surface smoothness of the magnetic tape. For calendar conditions, a calendar pressure is, for example, 200 to 500 kN/m and preferably 250 to 350 kN/m, a calendar temperature is, for example, 70° C. to 120° C. and preferably 80° C. to 100° C., and a calendar speed is, for example, 50 to 300 m/min and preferably 80 to 200 m/min. In addition, as a roll having a hard surface is used as a calendar roll, or as the number of stages is increased, the surface of the magnetic layer tends to be smoother.

For various other steps for manufacturing a magnetic tape, a description disclosed in paragraphs 0067 to 0070 of JP2010-231843A can be referred to.

Through various steps, a long magnetic tape raw material can be obtained. The obtained magnetic tape raw material is, for example, cut (slit) by a well-known cutter to have a width of a magnetic tape to be accommodated in the magnetic tape cartridge. The width can be determined according to the standard and is normally ½ inches. 1 inch=2.54 cm.

Burnishing Process

The burnishing process is a process of rubbing a surface of a process target with a member (for example, abrasive tape or a grinding tool such as a blade for grinding or a wheel for grinding). The burnishing process can be preferably performed by performing one or both of rubbing (polishing) of a surface of a coating layer which is a process target with an abrasive tape, and rubbing (grinding) of a surface of a coating layer which is a process target with a grinding tool. As the abrasive tape, a commercially available product may be used or an abrasive tape produced by a well-known method may be used. In addition, as the grinding tool, a well-known blade for grinding such as a fixed type blade, a diamond wheel, or a rotary blade, or a wheel for grinding can be used. Further, a wiping process of wiping the surface of the coating layer rubbed with the abrasive tape and/or the grinding tool with a wiping material may be performed. For details of the preferable abrasive tape, grinding tool, burnishing process, and wiping process, paragraphs 0034 to 0048, FIG. 1 , and examples of JP1994-052544A (JP-H06-052544A) can be referred to. The roughness of the surface to be treated can be controlled by the burnishing process, and as the burnishing process conditions are reinforced, the surface to be processed tends to be smooth. Examples of the burnishing process conditions include a tension applied in the longitudinal direction of the magnetic tape during the burnishing process (hereinafter, referred to as a “burnishing process tension”). The larger the value of the burnishing process tension, the smoother the surface to be processed tends to be. In order to control each of the edge portion Ra and the central portion Ra of the magnetic layer surface and to control the Ra ratio (central portion Ra/edge portion Ra) accordingly, it is preferable to perform the burnishing process on a central region of the surface of the magnetic layer and the burnishing process on a region in the vicinity of each edge (hereinafter, referred to as the “region in the vicinity of the edge”) under different process conditions, in a case of performing the burnishing process on the surface of the magnetic layer of the magnetic tape after the slitting. In the magnetic tape slit to a width of ½ inch, for example, the central region can be a region between the position of the inner side of 3 mm from the one edge and the position of the inner side of 3 mm from the other edge in the width direction of the magnetic tape, and a region other than such a central region can be referred to as the region in the vicinity of the edge. The central region and the region in the vicinity of the edge described with respect to the examples which will be described later are the regions described above.

For example, by making a value of a burnishing process tension during the burnishing process on the central region larger than a value of a burnishing process tension during the burnishing process on the region in the vicinity of the edge, the central region can be made smoother than the region in the vicinity of the edge, and as a result, the value of the edge portion Ra can be made larger than the value of the central portion Ra. In both the burnishing process on the central region and the burnishing process on the region in the vicinity of the edge, the burnishing process tension can be in a range of, for example, 50 gf to 250 gf, and a difference therebetween (the burnishing process tension in the central region—the burnishing process tension in the region in the vicinity of the edge) can be, for example, 3 gf to 30 gf. However, the range described above is an example and does not limit the present invention. In terms of unit, “gf” represents gram weight and 1 N (Newton) is approximately 102 gf.

Formation of Servo Pattern

In the magnetic tape obtained by slitting, a servo pattern can be generally formed. The formation of the servo pattern can be performed, for example, after the burnishing process described above (or even after the wiping process). The “formation of the servo pattern” can be “recording of a servo signal”. The formation of the servo pattern will be described below.

The servo pattern is generally formed along a longitudinal direction of the magnetic tape. As a system of control using a servo signal (servo control), timing-based servo (TBS), amplitude servo, or frequency servo is used.

As shown in European Computer Manufacturers Association (ECMA)-319 (June 2001), a timing-based servo system is used in a magnetic tape based on a linear tape-open (LTO) standard (generally referred to as an “LTO tape”). In this timing-based servo system, the servo pattern is configured by continuously disposing a plurality of pairs of magnetic stripes (also referred to as “servo stripes”) not parallel to each other in a longitudinal direction of the magnetic tape. In the invention and the specification, the “timing-based servo pattern” refers to a servo pattern that enables head tracking in a servo system of a timing-based servo system. As described above, a reason for that the servo pattern is configured with one pair of magnetic stripes not parallel to each other is because a servo signal reading element passing on the servo pattern recognizes a passage position thereof. Specifically, one pair of the magnetic stripes are formed so that a gap thereof is continuously changed along the width direction of the magnetic tape, and a relative position of the servo pattern and the servo signal reading element can be recognized, by the reading of the gap thereof by the servo signal reading element. The information of this relative position can realize the tracking of a data track. Accordingly, a plurality of servo tracks are generally set on the servo pattern along the width direction of the magnetic tape.

The servo band is configured of servo patterns continuous in the longitudinal direction of the magnetic tape. A plurality of servo bands are normally provided on the magnetic tape. For example, the number thereof is 5 in the LTO tape. A region interposed between two adjacent servo bands is a data band. The data band is configured of a plurality of data tracks and each data track corresponds to each servo track.

In one embodiment, as shown in JP2004-318983A, information showing the number of servo band (also referred to as “servo band identification (ID)” or “Unique Data Band Identification Method (UDIM) information”) is embedded in each servo band. This servo band ID is recorded by shifting a specific servo stripe among the plurality of pair of servo stripes in the servo band so that the position thereof is relatively deviated in the longitudinal direction of the magnetic tape. Specifically, the position of the shifted specific servo stripe among the plurality of pair of servo stripes is changed for each servo band. Accordingly, the recorded servo band ID becomes unique for each servo band, and therefore, the servo band can be uniquely specified by only reading one servo band by the servo signal reading element.

In a method of uniquely specifying the servo band, a staggered method as shown in ECMA-319 (June 2001) is used. In this staggered method, a plurality of the groups of one pair of magnetic stripes (servo stripe) not parallel to each other which are continuously disposed in the longitudinal direction of the magnetic tape is recorded so as to be shifted in the longitudinal direction of the magnetic tape for each servo band. A combination of this shifted servo band between the adjacent servo bands is set to be unique in the entire magnetic tape, and accordingly, the servo band can also be uniquely specified by reading of the servo pattern by two servo signal reading elements.

In addition, as shown in ECMA-319 (June 2001), information showing the position in the longitudinal direction of the magnetic tape (also referred to as “Longitudinal Position (LPOS) information”) is normally embedded in each servo band. This LPOS information is recorded so that the position of one pair of servo stripes is shifted in the longitudinal direction of the magnetic tape, in the same manner as the UDIM information. However, unlike the UDIM information, the same signal is recorded on each servo band in this LPOS information.

Other information different from the UDIM information and the LPOS information can be embedded in the servo band. In this case, the embedded information may be different for each servo band as the UDIM information, or may be common in all of the servo bands, as the LPOS information.

In addition, as a method of embedding the information in the servo band, a method other than the method described above can be used. For example, a predetermined code may be recorded by thinning out a predetermined pair among the group of pairs of the servo stripes.

A servo pattern forming head is also referred to as a servo write head. The servo write head generally includes pairs of gaps corresponding to the pairs of magnetic stripes by the number of servo bands. In general, a core and a coil are respectively connected to each of the pairs of gaps, and a magnetic field generated in the core can generate leakage magnetic field in the pairs of gaps, by supplying a current pulse to the coil. In a case of forming the servo pattern, by inputting a current pulse while causing the magnetic tape to run on the servo write head, the magnetic pattern corresponding to the pair of gaps is transferred to the magnetic tape, and the servo pattern can be formed. A width of each gap can be suitably set in accordance with a density of the servo pattern to be formed. The width of each gap can be set as, for example, equal to or smaller than 1 μm, 1 to 10 μm, or equal to or greater than 10 μm.

Before forming the servo pattern on the magnetic tape, a demagnetization (erasing) process is generally performed on the magnetic tape. This erasing process can be performed by applying a uniform magnetic field to the magnetic tape by using a DC magnet and an AC magnet. The erasing process includes direct current (DC) erasing and alternating current (AC) erasing. The AC erasing is performed by slowing decreasing an intensity of the magnetic field, while reversing a direction of the magnetic field applied to the magnetic tape. Meanwhile, the DC erasing is performed by applying the magnetic field in one direction to the magnetic tape. The DC erasing further includes two methods. A first method is horizontal DC erasing of applying the magnetic field in one direction along a longitudinal direction of the magnetic tape. A second method is vertical DC erasing of applying the magnetic field in one direction along a thickness direction of the magnetic tape. The erasing process may be performed with respect to all of the magnetic tape or may be performed for each servo band of the magnetic tape.

A direction of the magnetic field to the servo pattern to be formed is determined in accordance with the direction of erasing. For example, in a case where the horizontal DC erasing is performed to the magnetic tape, the formation of the servo pattern is performed so that the direction of the magnetic field and the direction of erasing is opposite to each other. Accordingly, the output of the servo signal obtained by the reading of the servo pattern can be increased. As disclosed in JP2012-53940A, in a case where the magnetic pattern is transferred to the magnetic tape subjected to the vertical DC erasing by using the gap, the servo signal obtained by the reading of the formed servo pattern has a unipolar pulse shape. Meanwhile, in a case where the magnetic pattern is transferred to the magnetic tape subjected to the horizontal DC erasing by using the gap, the servo signal obtained by the reading of the formed servo pattern has a bipolar pulse shape.

Heat Treatment

In one embodiment, the magnetic tape can be a magnetic tape manufactured through the following heat treatment. In another aspect, the magnetic tape can be manufactured without the following heat treatment.

The heat treatment can be performed in a state where the magnetic tape slit and cut to have a width determined according to the standard is wound around a core member.

In one embodiment, the heat treatment is performed in a state where the magnetic tape is wound around the core member for heat treatment (hereinafter, referred to as a “core for heat treatment”), the magnetic tape after the heat treatment is wound around a cartridge reel of the magnetic tape cartridge, and a magnetic tape cartridge in which the magnetic tape is wound around the cartridge reel can be manufactured.

The core for heat treatment can be formed of metal, a resin, or paper. The material of the core for heat treatment is preferably a material having high stiffness, from a viewpoint of preventing the occurrence of a winding defect such as spoking or the like. From this viewpoint, the core for heat treatment is preferably formed of metal or a resin. In addition, as an index for stiffness, a bending elastic modulus of the material for the core for heat treatment is preferably equal to or greater than 0.2 GPa (gigapascal) and more preferably equal to or greater than 0.3 GPa. Meanwhile, since the material having high stiffness is normally expensive, the use of the core for heat treatment of the material having stiffness exceeding the stiffness capable of preventing the occurrence of the winding defect causes the cost increase. By considering the viewpoint described above, the bending elastic modulus of the material for the core for heat treatment is preferably equal to or smaller than 250 GPa. The bending elastic modulus is a value measured based on international organization for standardization (ISO) 178 and the bending elastic modulus of various materials is well known. In addition, the core for heat treatment can be a solid or hollow core member. In a case of a hollow shape, a wall thickness is preferably equal to or greater than 2 mm, from a viewpoint of maintaining the stiffness. In addition, the core for heat treatment may include or may not include a flange.

The magnetic tape having a length equal to or greater than a length to be finally accommodated in the magnetic tape cartridge (hereinafter, referred to as a “final product length”) is prepared as the magnetic tape wound around the core for heat treatment, and it is preferable to perform the heat treatment by placing the magnetic tape in the heat treatment environment, in a state where the magnetic tape is wound around the core for heat treatment. The magnetic tape length wound around the core for heat treatment is equal to or greater than the final product length, and is preferably the “final product length+α”, from a viewpoint of ease of winding around the core for heat treatment. This a is preferably equal to or greater than 5 m, from a viewpoint of ease of the winding. The tension in a case of winding around the core for heat treatment is preferably equal to or greater than 0.1 N (newton). In addition, from a viewpoint of preventing the occurrence of excessive deformation during the manufacturing, the tension in a case of winding around the core for heat treatment is preferably equal to or smaller than 1.5 N and more preferably equal to or smaller than 1.0 N. An outer diameter of the core for heat treatment is preferably equal to or greater than 20 mm and more preferably equal to or greater than 40 mm, from viewpoints of ease of the winding and preventing coiling (curl in longitudinal direction). The outer diameter of the core for heat treatment is preferably equal to or smaller than 100 mm and more preferably equal to or smaller than 90 mm. A width of the core for heat treatment may be equal to or greater than the width of the magnetic tape wound around this core. In addition, after the heat treatment, in a case of detaching the magnetic tape from the core for heat treatment, it is preferable that the magnetic tape and the core for heat treatment are sufficiently cooled and magnetic tape is detached from the core for heat treatment, in order to prevent the occurrence of the tape deformation which is not intended during the detaching operation. It is preferable the detached magnetic tape is wound around another core temporarily (referred to as a “core for temporary winding”), and the magnetic tape is wound around a cartridge reel (generally, outer diameter is approximately 40 to 50 mm) of the magnetic tape cartridge from the core for temporary winding. Accordingly, a relationship between the inside and the outside with respect to the core for heat treatment of the magnetic tape in a case of the heat treatment can be maintained and the magnetic tape can be wound around the cartridge reel of the magnetic tape cartridge. Regarding the details of the core for temporary winding and the tension in a case of winding the magnetic tape around the core, the description described above regarding the core for heat treatment can be referred to. In an embodiment in which the heat treatment is subjected to the magnetic tape having a length of the “final product length+α”, the length corresponding to “+α” may be cut in any stage. For example, In one embodiment, the magnetic tape having the final product length may be wound around the cartridge reel of the magnetic tape cartridge from the core for temporary winding and the remaining length corresponding the “+α” may be cut. From a viewpoint of decreasing the amount of the portion to be cut out and removed, the α is preferably equal to or smaller than 20 m.

The specific embodiment of the heat treatment performed in a state of being wound around the core member as described above is described below.

An atmosphere temperature for performing the heat treatment (hereinafter, referred to as a “heat treatment temperature”) is preferably equal to or higher than 40° C. and more preferably equal to or higher than 50° C. On the other hand, from a viewpoint of preventing the excessive deformation, the heat treatment temperature is preferably equal to or lower than 75° C. and more preferably equal to or lower than 70° C.

A weight absolute humidity of the atmosphere for performing the heat treatment is preferably equal to or greater than 0.1 g/kg Dry air and more preferably equal to or greater than 1 g/kg Dry air. The atmosphere in which the weight absolute humidity is in the range described above is preferable, because it can be prepared without using a special device for decreasing moisture. On the other hand, the weight absolute humidity is preferably equal to or smaller than 70 g/kg Dry air and more preferably equal to or smaller than 66 g/kg Dry air, from a viewpoint of preventing a deterioration in workability by dew condensation. The heat treatment time is preferably equal to or longer than 0.3 hours and more preferably equal to or longer than 0.5 hours. In addition, the heat treatment time is preferably equal to or shorter than 48 hours, from a viewpoint of production efficiency.

Regarding the control of the standard deviation of the curvature described above, as any value of the heat treatment temperature, heat treatment time, bending elastic modulus of a core for the heat treatment, and tension at the time of winding around the core for the heat treatment is large, the value of the curvature tends to further decrease.

<Vertical Squareness Ratio>

In one embodiment, the vertical squareness ratio of the magnetic tape can be, for example, 0.55 or more, and is preferably 0.60 or more. It is preferable that the vertical squareness ratio of the magnetic tape is 0.60 or more, from a viewpoint of improving the electromagnetic conversion characteristics. In principle, an upper limit of the squareness ratio is 1.00 or less. The vertical squareness ratio of the magnetic tape can be 1.00 or less, 0.95 or less, 0.90 or less, 0.85 or less, or 0.80 or less. It is preferable that the value of the vertical squareness ratio of the magnetic tape is large from a viewpoint of improving the electromagnetic conversion characteristics. The vertical squareness ratio of the magnetic tape can be controlled by a well-known method such as performing a homeotropic alignment process.

In the invention and the specification, the “vertical squareness ratio” is squareness ratio measured in the vertical direction of the magnetic tape. The “vertical direction” described with respect to the squareness ratio is a direction orthogonal to the surface of the magnetic layer, and can also be referred to as a thickness direction. In the invention and the specification, the vertical squareness ratio is obtained by the following method.

A sample piece having a size that can be introduced into an oscillation sample type magnetic-flux meter is cut out from the magnetic tape to be measured. Regarding the sample piece, using the oscillation sample type magnetic-flux meter, a magnetic field is applied to a vertical direction of a sample piece (direction orthogonal to the surface of the magnetic layer) with a maximum applied magnetic field of 3979 kA/m, a measurement temperature of 296 K, and a magnetic field sweep speed of 8.3 kA/m/sec, and a magnetization strength of the sample piece with respect to the applied magnetic field is measured. The measured value of the magnetization strength is obtained as a value after diamagnetic field correction and a value obtained by subtracting magnetization of a sample probe of the oscillation sample type magnetic-flux meter as background noise. In a case where the magnetization strength at the maximum applied magnetic field is Ms and the magnetization strength at zero applied magnetic field is Mr, the squareness ratio SQ is a value calculated as SQ=Mr/Ms. The measurement temperature is referred to as a temperature of the sample piece, and by setting the ambient temperature around the sample piece to a measurement temperature, the temperature of the sample piece can be set to the measurement temperature by realizing temperature equilibrium.

Magnetic Tape Cartridge

According to another aspect of the invention, there is provided a magnetic tape cartridge comprising the magnetic tape described above.

The details of the magnetic tape included in the magnetic tape cartridge are as described above.

In the magnetic tape cartridge, the magnetic tape is generally accommodated in a cartridge main body in a state of being wound around a reel. The reel is rotatably provided in the cartridge main body. As the magnetic tape cartridge, a single reel type magnetic tape cartridge including one reel in a cartridge main body and a twin reel type magnetic tape cartridge including two reels in a cartridge main body are widely used. In a case where the single reel type magnetic tape cartridge is mounted in the magnetic tape device in order to record and/or reproduce data on the magnetic tape, the magnetic tape is drawn from the magnetic tape cartridge and wound around the reel on the magnetic tape device side. A magnetic head is disposed on a magnetic tape transportation path from the magnetic tape cartridge to a winding reel. Feeding and winding of the magnetic tape are performed between a reel (supply reel) on the magnetic tape cartridge side and a reel (winding reel) on the magnetic tape device side. In the meantime, for example, the magnetic head comes into contact with and slides on the surface of the magnetic layer of the magnetic tape, and accordingly, the recording and/or reproducing of data is performed. With respect to this, in the twin reel type magnetic tape cartridge, both reels of the supply reel and the winding reel are provided in the magnetic tape cartridge.

In one embodiment, the magnetic tape cartridge can include a cartridge memory. The cartridge memory can be, for example, a non-volatile memory, and in one embodiment, head tilt angle adjustment information is recorded in advance or head tilt angle adjustment information is recorded. The head tilt angle adjustment information is information for adjusting the head tilt angle during the running of the magnetic tape in the magnetic tape device. For example, as the head tilt angle adjustment information, a value of the servo band spacing at each position in the longitudinal direction of the magnetic tape at the time of data recording can be recorded. For example, in a case where the data recorded on the magnetic tape is reproduced, the value of the servo band spacing is measured at the time of the reproducing, and the head tilt angle can be changed by the control device of the magnetic tape device so that an absolute value of a difference of the servo band spacing at the time of recording at the same longitudinal position recorded in the cartridge memory is close to 0. The head tilt angle can be, for example, the angle θ described above.

The magnetic tape and the magnetic tape cartridge can be suitably used in the magnetic tape device (that is, magnetic recording and reproducing system) for performing recording and/or reproducing data at different head tilt angles. In such a magnetic tape device, in one embodiment, it is possible to perform the recording and/or reproducing of data by changing the head tilt angle during running of a magnetic tape. For example, the head tilt angle can be changed according to dimensional information of the magnetic tape in the width direction obtained while the magnetic tape is running. In addition, for example, in a usage aspect, a head tilt angle during the recording and/or reproducing at a certain time and a head tilt angle during the recording and/or reproducing at the next time and subsequent times are changed, and then the head tilt angle may be fixed without changing during the running of the magnetic tape for the recording and/or reproducing of each time. In any usage aspect, a magnetic tape having high running stability in a case of performing the recording and/or reproducing of data at different head tilt angles is preferable.

Magnetic Tape Device

According to still another aspect of the invention, there is provided a magnetic tape device comprising the magnetic tape. In the magnetic tape device, the recording of data on the magnetic tape and/or the reproducing of data recorded on the magnetic tape can be performed by bringing the surface of the magnetic layer of the magnetic tape into contact with the magnetic head and sliding. For example, the magnetic tape device can attachably and detachably include the magnetic tape cartridge according to one embodiment of the invention.

The magnetic tape cartridge can be attached to a magnetic tape device provided with a magnetic head and used for performing the recording and/or reproducing of data. In the invention and the specification, the “magnetic tape device” means a device capable of performing at least one of the recording of data on the magnetic tape or the reproducing of data recorded on the magnetic tape. Such a device is generally called a drive.

Magnetic Head

The magnetic tape device can include a magnetic head. The configuration of the magnetic head and the angle θ, which is the head tilt angle, are as described above with reference to FIGS. 1 to 3 . In a case where the magnetic head includes a reproducing element, as the reproducing element, a magnetoresistive (MR) element capable of reading information recorded on the magnetic tape with excellent sensitivity is preferable. As the MR element, various well-known MR elements (for example, a Giant Magnetoresistive (GMR) element, or a Tunnel Magnetoresistive (TMR) element) can be used. Hereinafter, the magnetic head which records data and/or reproduces the recorded data is also referred to as a “recording and reproducing head”. The element for recording data (recording element) and the element for reproducing data (reproducing element) are collectively referred to as a “magnetic head element”.

By reproducing data using the reproducing element having a narrow reproducing element width as the reproducing element, the data recorded at high density can be reproduced with high sensitivity. From this viewpoint, the reproducing element width of the reproducing element is preferably 0.8 μm or less. The reproducing element width of the reproducing element can be, for example, 0.3 μm or more. However, it is also preferable to fall below this value from the above viewpoint.

Here, the “reproducing element width” refers to a physical dimension of the reproducing element width. Such physical dimensions can be measured with an optical microscope, a scanning electron microscope, or the like.

In a case of recording data and/or reproducing recorded data, first, tracking using a servo signal can be performed. That is, as the servo signal reading element follows a predetermined servo track, the magnetic head element can be controlled to pass on the target data track. The movement of the data track is performed by changing the servo track to be read by the servo signal reading element in the tape width direction.

In addition, the recording and reproducing head can perform the recording and/or reproducing with respect to other data bands. In this case, the servo signal reading element is moved to a predetermined servo band by using the UDIM information described above, and the tracking with respect to the servo band may be started.

FIG. 5 shows an example of disposition of data bands and servo bands. In FIG. 5 , a plurality of servo bands 1 are disposed to be interposed between guide bands 3 in a magnetic layer of a magnetic tape MT. A plurality of regions 2 each of which is interposed between two servo bands are data bands. The servo pattern is a magnetized region and is formed by magnetizing a specific region of the magnetic layer by a servo write head. The region magnetized by the servo write head (position where a servo pattern is formed) is determined by standards. For example, in an LTO Ultrium format tape which is based on a local standard, a plurality of servo patterns tilted in a tape width direction as shown in FIG. 6 are formed on a servo band, in a case of manufacturing a magnetic tape. Specifically, in FIG. 6 , a servo frame SF on the servo band 1 is configured with a servo sub-frame 1 (SSF1) and a servo sub-frame 2 (SSF2). The servo sub-frame 1 is configured with an A burst (in FIG. 6 , reference numeral A) and a B burst (in FIG. 6 , reference numeral B). The A burst is configured with servo patterns A1 to A5 and the B burst is configured with servo patterns B1 to B5. Meanwhile, the servo sub-frame 2 is configured with a C burst (in FIG. 6 , reference numeral C) and a D burst (in FIG. 6 , reference numeral D). The C burst is configured with servo patterns C1 to C4 and the D burst is configured with servo patterns D1 to D4. Such 18 servo patterns are disposed in the sub-frames in the arrangement of 5, 5, 4, 4, as the sets of 5 servo patterns and 4 servo patterns, and are used for recognizing the servo frames. FIG. 6 shows one servo frame for explaining. However, in practice, in the magnetic layer of the magnetic tape in which the head tracking in the timing-based servo system is performed, a plurality of servo frames are disposed in each servo band in a running direction. In FIG. 6 , an arrow shows a magnetic tape running direction. For example, an LTO Ultrium format tape generally includes 5,000 or more servo frames per a tape length of 1 m, in each servo band of the magnetic layer.

In the magnetic tape device, the head tilt angle can be changed while the magnetic tape is running in the magnetic tape device. The head tilt angle is, for example, an angle θ formed by the axis of the element array with respect to the width direction of the magnetic tape. The angle θ is as described above. For example, by providing an angle adjustment unit for adjusting the angle of the module of the magnetic head in the recording and reproducing head unit of the magnetic head, the angle θ can be variably adjusted during the running of the magnetic tape. Such an angle adjustment unit can include, for example, a rotation mechanism for rotating the module. For the angle adjustment unit, a well-known technology can be applied.

Regarding the head tilt angle during the running of the magnetic tape, in a case where the magnetic head includes a plurality of modules, the angle θ described with reference to FIGS. 1 to 3 can be specified for the randomly selected module. The angle θ at the start of running of the magnetic tape, θ_(initial), can be set to 0° or more or more than 0°. As the θ_(initial) is large, a change amount of the effective distance between the servo signal reading elements with respect to a change amount of the angle θ increases, and accordingly, it is preferable from a viewpoint of adjustment ability for adjusting the effective distance between the servo signal reading elements according to the dimension change of the width direction of the magnetic tape. From this viewpoint, the ° initial is preferably 1° or more, more preferably 5° or more, and even more preferably 10° or more. Meanwhile, regarding an angle (generally referred to as a “lap angle”) formed by a surface of the magnetic layer and a contact surface of the magnetic head in a case where the magnetic tape runs and comes into contact with the magnetic head, a deviation in a tape width direction which is kept small is effective in improving uniformity of friction in the tape width direction which is generated by the contact between the magnetic head and the magnetic tape during the running of the magnetic tape. In addition, it is desirable to improve the uniformity of the friction in the tape width direction from a viewpoint of position followability and the running stability of the magnetic head. From a viewpoint of reducing the deviation of the lap angle in the tape width direction, θ_(initial) is preferably 45° or less, more preferably 40° or less, and even more preferably 35° or less.

Regarding the change of the angle θ during the running of the magnetic tape, while the magnetic tape is running in the magnetic tape device in order to record data on the magnetic tape and/or to reproduce data recorded on the magnetic tape, in a case where the angle θ of the magnetic head changes from θ_(initial) at the start of running, a maximum change amount Δθ of the angle θ during the running of the magnetic tape is a larger value among Δθ_(max) and Δθ_(min) calculated by the following equation. A maximum value of the angle θ during the running of the magnetic tape is θ_(max), and a minimum value thereof is θ_(min). In addition, “max” is an abbreviation for maximum, and “min” is an abbreviation for minimum. Δθ_(max)=θ_(max)−θ_(initial) Δθ_(min)=θ_(initial)−θ_(min)

In one embodiment, the Δθ can be more than 0.000°, and is preferably 0.001° or more and more preferably 0.010° or more, from a viewpoint of adjustment ability for adjusting the effective distance between the servo signal reading elements according to the dimension change in the width direction of the magnetic tape. In addition, from a viewpoint of ease of ensuring synchronization of recorded data and/or reproduced data between a plurality of magnetic head elements during data recording and/or reproducing, the Δθ is preferably 1.000° or less, more preferably 0.900° or less, even more preferably 0.800° or less, still preferably 0.700° or less, and still more preferably 0.600° or less.

In the examples shown in FIGS. 2 and 3 , the axis of the element array is tilted toward a magnetic tape running direction. However, the present invention is not limited to such an example. The present invention also includes an embodiment in which the axis of the element array is tilted in a direction opposite to the magnetic tape running direction in the magnetic tape device.

The head tilt angle θ_(initial) at the start of the running of the magnetic tape can be set by a control device or the like of the magnetic tape device.

Regarding the head tilt angle during the running of the magnetic tape, FIG. 7 is an explanatory diagram of a method for measuring the angle θ during the running of the magnetic tape. The angle θ during the running of the magnetic tape can be obtained, for example, by the following method. In a case where the angle θ during traveling on the magnetic tape is obtained by the following method, the angle θ is changed in a range of 0° to 90° during the running of the magnetic tape. That is, in a case where the axis of the element array is tilted toward the magnetic tape running direction at the start of running of the magnetic tape, the element array is not tilted so that the axis of the element array tilts toward a direction opposite to the magnetic tape running direction at the start of the running of the magnetic tape, during the running of the magnetic tape, and in a case where the axis of the element array is tilted toward the direction opposite to the magnetic tape running direction at the start of running of the magnetic tape, the element array is not tilted so that the axis of the element array tilts toward the magnetic tape running direction at the start of the running of the magnetic tape, during the running of the magnetic tape.

A phase difference (that is, time difference) ΔT of reproduction signals of the pair of servo signal reading elements 1 and 2 is measured. The measurement of ΔT can be performed by a measurement unit provided in the magnetic tape device. A configuration of such a measurement unit is well known. A distance L between a central portion of the servo signal reading element 1 and a central portion of the servo signal reading element 2 can be measured with an optical microscope or the like. In a case where a running speed of the magnetic tape is defined as a speed v, the distance in the magnetic tape running direction between the central portions of the two servo signal reading elements is set to L sin θ, and a relationship of L sin θ=v×ΔT is satisfied. Therefore, the angle θ during the running of the magnetic tape can be calculated by a formula “θ=arcsin (vΔT/L)”. The right drawing of FIG. 7 shows an example in which the axis of the element array is tilted toward the magnetic tape running direction. In this example, the phase difference (that is, time difference) ΔT of a phase of the reproduction signal of the servo signal reading element 2 with respect to a phase of the reproduction signal of the servo signal reading element 1 is measured. In a case where the axis of the element array is tilted toward the direction opposite to the running direction of the magnetic tape, θ can be obtained by the method described above, except for measuring ΔT as the phase difference (that is, time difference) of the phase of the reproduction signal of the servo signal reading element 1 with respect to the phase of the reproduction signal of the servo signal reading element 2.

For a measurement pitch of the angle θ, that is, a measurement interval of the angle θ in a tape longitudinal direction, a suitable pitch can be selected according to a frequency of tape width deformation in the tape longitudinal direction. As an example, the measurement pitch can be, for example, 250 μm.

Configuration of Magnetic Tape Device

A magnetic tape device 10 shown in FIG. 8 controls a recording and reproducing head unit 12 in accordance with a command from a control device 11 to record and reproduce data on a magnetic tape MT.

The magnetic tape device 10 has a configuration of detecting and adjusting a tension applied in a longitudinal direction of the magnetic tape from spindle motors 17A and 17B and driving devices 18A and 18B which rotatably control a magnetic tape cartridge reel and a winding reel.

The magnetic tape device 10 has a configuration in which the magnetic tape cartridge 13 can be mounted.

The magnetic tape device 10 includes a cartridge memory read and write device 14 capable of performing reading and writing with respect to the cartridge memory 131 in the magnetic tape cartridge 13.

An end portion or a leader pin of the magnetic tape MT is pulled out from the magnetic tape cartridge 13 mounted on the magnetic tape device 10 by an automatic loading mechanism or manually and passes on a recording and reproducing head through guide rollers 15A and 15B so that a surface of a magnetic layer of the magnetic tape MT comes into contact with a surface of the recording and reproducing head of the recording and reproducing head unit 12, and accordingly, the magnetic tape MT is wound around the winding reel 16.

The rotation and torque of the spindle motor 17A and the spindle motor 17B are controlled by a signal from the control device 11, and the magnetic tape MT runs at random speed and tension. A servo pattern previously formed on the magnetic tape can be used to control the tape speed and control the head tilt angle. A tension detection mechanism may be provided between the magnetic tape cartridge 13 and the winding reel 16 to detect the tension. The tension may be controlled by using the guide rollers 15A and 15B in addition to the control by the spindle motors 17A and 17B.

The cartridge memory read and write device 14 is configured to be able to read and write information of the cartridge memory 131 according to commands from the control device 11. As a communication system between the cartridge memory read and write device 14 and the cartridge memory 131, for example, an international organization for standardization (ISO) 14443 system can be used.

The control device 11 includes, for example, a controller, a storage unit, a communication unit, and the like.

The recording and reproducing head unit 12 is composed of, for example, a recording and reproducing head, a servo tracking actuator for adjusting a position of the recording and reproducing head in a track width direction, a recording and reproducing amplifier 19, a connector cable for connecting to the control device 11. The recording and reproducing head is composed of, for example, a recording element for recording data on a magnetic tape, a reproducing element for reproducing data of the magnetic tape, and a servo signal reading element for reading a servo signal recorded on the magnetic tape. For example, one or more of each of the recording elements, the reproducing element, and the servo signal reading element are mounted in one magnetic head. Alternatively, each element may be separately provided in a plurality of magnetic heads according to a running direction of the magnetic tape.

The recording and reproducing head unit 12 is configured to be able to record data on the magnetic tape MT according to a command from the control device 11. In addition, the data recorded on the magnetic tape MT can be reproduced according to a command from the control device 11.

The control device 11 has a mechanism of controlling the servo tracking actuator so as to obtain a running position of the magnetic tape from a servo signal read from a servo band during the running of the magnetic tape MT and position the recording element and/or the reproducing element at a target running position (track position). The control of the track position is performed by feedback control, for example. The control device 11 has a mechanism of obtaining a servo band spacing from servo signals read from two adjacent servo bands during the running of the magnetic tape MT. The control device 11 can store the obtained information of the servo band spacing in the storage unit inside the control device 11, the cartridge memory 131, an external connection device, and the like. In addition, the control device 11 can change the head tilt angle according to the dimensional information in the width direction of the magnetic tape during the running. Accordingly, it is possible to bring the effective distance between the servo signal reading elements closer to or match the spacing of the servo bands. The dimensional information can be obtained by using the servo pattern previously formed on the magnetic tape. For example, by doing so, the angle θ formed by the axis of the element array with respect to the width direction of the magnetic tape can be changed during the running of the magnetic tape in the magnetic tape device according to dimensional information of the magnetic tape in the width direction obtained during the running. The head tilt angle can be adjusted, for example, by feedback control. Alternatively, for example, the head tilt angle can also be adjusted by a method disclosed in JP2016-524774A or US2019/0164573A1.

EXAMPLES

Hereinafter, the invention will be described with reference to examples. However, the invention is not limited to the embodiments shown in the examples. “Parts” and “%” described below indicate “parts by mass” and “% by mass”. In addition, steps and evaluations described below are performed in an environment of an atmosphere temperature of 23° C.±1° C., unless otherwise noted. “eq” described below indicates equivalent and a unit not convertible into SI unit.

Ferromagnetic Powder

In Table 1, “BaFe” is a hexagonal barium ferrite powder (coercivity Hc: 196 kA/m, an average particle size (average plate diameter): 24 nm).

In Table 1, “SrFe1” is a hexagonal strontium ferrite powder produced by the following method.

1,707 g of SrCO₃, 687 g of H₃BO₃, 1,120 g of Fe₂O₃, 45 g of Al(OH)₃, 24 g of BaCO₃, 13 g of CaCO₃, and 235 g of Nd₂O₃ were weighed and mixed in a mixer to obtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucible at a melting temperature of 1,390° C., and a tap hole provided on the bottom of the platinum crucible was heated while stirring the melt, and the melt was tapped in a rod shape at approximately 6 g/sec. The tap liquid was rolled and cooled with a water cooling twin roller to prepare an amorphous body.

280 g of the prepared amorphous body was put into an electronic furnace, heated to 635° C. (crystallization temperature) at a rate of temperature rise of 3.5° C./min, and held at the same temperature for 5 hours, and hexagonal strontium ferrite particles were precipitated (crystallized).

Then, the crystallized material obtained as described above including the hexagonal strontium ferrite particles was coarse-pulverized with a mortar, 1000 g of zirconia beads having a particle diameter of 1 mm and 800 ml of an acetic acid aqueous solution having a concentration of 1% were added to a glass bottle, and a dispersion process was performed in a paint shaker for 3 hours. After that, the obtained dispersion liquid and the beads were separated and put in a stainless still beaker. The dispersion liquid was left at a liquid temperature of 100° C. for 3 hours, subjected to a dissolving process of a glass component, precipitated with a centrifugal separator, decantation was repeated for cleaning, and drying was performed in a heating furnace at a furnace inner temperature of 110° C. for 6 hours, to obtain hexagonal strontium ferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as described above, an average particle size was 18 nm, an activation volume was 902 nm³, an anisotropy constant Ku was 2.2×10⁵ J/m³, and a mass magnetization σs was 49 A·m²/kg.

12 mg of a sample powder was collected from the hexagonal strontium ferrite powder obtained as described above, the element analysis of a filtrate obtained by the partial dissolving of this sample powder under the dissolving conditions described above was performed by the ICP analysis device, and a surface layer portion content of a neodymium atom was obtained.

Separately, 12 mg of a sample powder was collected from the hexagonal strontium ferrite powder obtained as described above, the element analysis of a filtrate obtained by the total dissolving of this sample powder under the dissolving conditions described above was performed by the ICP analysis device, and a bulk content of a neodymium atom was obtained.

The content (bulk content) of the neodymium atom in the hexagonal strontium ferrite powder obtained as described above with respect to 100 atom % of iron atom was 2.9 atom %. In addition, the surface layer portion content of the neodymium atom was 8.0 atom %. A ratio of the surface layer portion content and the bulk content, “surface layer portion content/bulk content” was 2.8 and it was confirmed that the neodymium atom is unevenly distributed on the surface layer of the particles.

A crystal structure of the hexagonal ferrite shown by the powder obtained as described above was confirmed by scanning CuKα ray under the conditions of a voltage of 45 kV and intensity of 40 mA and measuring an X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). The powder obtained as described above showed a crystal structure of magnetoplumbite type (M type) hexagonal ferrite. In addition, a crystal phase detected by the X-ray diffraction analysis was a magnetoplumbite type single phase.

PANalytical X'Pert Pro diffractometer, PIXcel detector

Soller slit of incident beam and diffraction beam: 0.017 radians

Fixed angle of dispersion slit: ¼ degrees

Mask: 10 mm

Scattering prevention slit: ¼ degrees

Measurement mode: continuous

Measurement time per 1 stage: 3 seconds

Measurement speed: 0.017 degrees per second

Measurement step: 0.05 degree

In Table 1, “SrFe2” is a hexagonal strontium ferrite powder produced by the following method.

1,725 g of SrCO₃, 666 g of H₃BO₃, 1,332 g of Fe₂O₃, 52 g of Al(OH)₃, 34 g of CaCO₃, and 141 g of BaCO₃ were weighed and mixed in a mixer to obtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucible at a melting temperature of 1,380° C., and a tap hole provided on the bottom of the platinum crucible was heated while stirring the melt, and the melt was tapped in a rod shape at approximately 6 g/sec. The tap liquid was rolled and cooled with a water cooling twin roller to prepare an amorphous body.

280 g of the obtained amorphous body was put into an electronic furnace, heated to 645° C. (crystallization temperature), and held at the same temperature for 5 hours, and hexagonal strontium ferrite particles were precipitated (crystallized).

Then, the crystallized material obtained as described above including the hexagonal strontium ferrite particles was coarse-pulverized with a mortar, 1000 g of zirconia beads having a particle diameter of 1 mm and 800 ml of an acetic acid aqueous solution having a concentration of 1% were added to a glass bottle, and a dispersion process was performed in a paint shaker for 3 hours. After that, the obtained dispersion liquid and the beads were separated and put in a stainless still beaker. The dispersion liquid was left at a liquid temperature of 100° C. for 3 hours, subjected to a dissolving process of a glass component, precipitated with a centrifugal separator, decantation was repeated for cleaning, and drying was performed in a heating furnace at a furnace inner temperature of 110° C. for 6 hours, to obtain hexagonal strontium ferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as described above, an average particle size was 19 nm, an activation volume was 1,102 nm³, an anisotropy constant Ku was 2.0×10⁵ J/m³, and a mass magnetization σs was 50 A×m²/kg.

In Table 1, “ε-iron oxide” is an ε-iron oxide powder produced by the following method.

4.0 g of ammonia aqueous solution having a concentration of 25% was added to a material obtained by dissolving 8.3 g of iron (III) nitrate nonahydrate, 1.3 g of gallium (III) nitrate octahydrate, 190 mg of cobalt (II) nitrate hexahydrate, 150 mg of titanium (IV) sulfate, and 1.5 g of polyvinyl pyrrolidone (PVP) in 90 g of pure water, while stirring by using a magnetic stirrer, in an atmosphere under the conditions of an atmosphere temperature of 25° C., and the mixture was stirred for 2 hours still under the temperature condition of the atmosphere temperature of 25° C. A citric acid aqueous solution obtained by dissolving 1 g of citric acid in 9 g of pure water was added to the obtained solution and stirred for 1 hour. The powder precipitated after the stirring was collected by centrifugal separation, washed with pure water, and dried in a heating furnace at a furnace inner temperature of 80° C.

800 g of pure water was added to the dried powder and the powder was dispersed in water again, to obtain a dispersion liquid. The obtained dispersion liquid was heated to a liquid temperature of 50° C., and 40 g of ammonia aqueous solution having a concentration of 25% was added dropwise while stirring. The stirring was performed for 1 hour while holding the temperature of 50° C., and 14 mL of tetraethoxysilane (TEOS) was added dropwise and stirred for 24 hours. 50 g of ammonium sulfate was added to the obtained reaction solution, the precipitated powder was collected by centrifugal separation, washed with pure water, and dried in a heating furnace at a furnace inner temperature of 80° C. for 24 hours, and a precursor of ferromagnetic powder was obtained.

The heating furnace at a furnace inner temperature of 1,000° C. was filled with the obtained precursor of ferromagnetic powder in the atmosphere and subjected to heat treatment for 4 hours.

The heat-treated precursor of ferromagnetic powder was put into sodium hydroxide (NaOH) aqueous solution having a concentration of 4 mol/L, the liquid temperature was held at 70° C., stirring was performed for 24 hours, and accordingly, a silicon acid compound which was an impurity was removed from the heat-treated precursor of ferromagnetic powder.

After that, by the centrifugal separation process, ferromagnetic powder obtained by removing the silicon acid compound was collected and washed with pure water, and ferromagnetic powder was obtained.

The composition of the obtained ferromagnetic powder was confirmed by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), and Ga, Co, and Ti substitution type ε-iron oxide (ε-Ga_(0.28)Co_(0.05)Ti_(0.05)Fe_(1.62)O₃) was obtained. In addition, the X-ray diffraction analysis was performed under the same conditions as disclosed regarding SrFe1 above, and it was confirmed that the obtained ferromagnetic powder has a crystal structure of a single phase which is an E phase not including a crystal structure of an α phase and a γ phase (ε-iron oxide type crystal structure) from the peak of the X-ray diffraction pattern.

Regarding the obtained (ε-iron oxide powder, an average particle size was 12 nm, an activation volume was 746 nm³, an anisotropy constant Ku was 1.2×10⁵ J/m³, and a mass magnetization σs was 16 A×m²/kg.

The activation volume and the anisotropy constant Ku of the hexagonal strontium ferrite powder and the ε-iron oxide powder are values obtained by the method described above regarding each ferromagnetic powder by using an oscillation sample type magnetic-flux meter (manufactured by Toei Industry Co., Ltd.).

The mass magnetization σs is a value measured using a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.) at a magnetic field strength of 15 kOe.

Example 1

Preparation of Alumina Dispersion

3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry Co., Ltd.), 31.3 parts of a 32% solution (solvent is a mixed solvent of methyl ethyl ketone and toluene) of a polyester polyurethane resin including a SO₃Na group as a polar group (UR-4800 manufactured by Toyobo Co., Ltd. (polar group amount: 80 meq/kg)), and 570.0 parts of a mixed solution of methyl ethyl ketone and cyclohexanone (mass ratio of 1:1) as a solvent were mixed with 100.0 parts of alumina powder (HIT-80 manufactured by Sumitomo Chemical Co., Ltd.) having a gelatinization ratio of 65% and a Brunauer-Emmett-Teller (BET) specific surface area of 20 m²/g, and dispersed in the presence of zirconia beads by a paint shaker for 5 hours. After the dispersion, the dispersion liquid and the beads were separated by a mesh and an alumina dispersion was obtained.

Magnetic Layer Forming Composition

Magnetic Liquid

Ferromagnetic powder (see Table 1): 100.0 parts

SO₃Na group-containing polyurethane resin: 14.0 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g

Cyclohexanone: 150.0 parts

Methyl ethyl ketone: 150.0 parts

Abrasive solution

Alumina dispersion prepared above: 6.0 parts

Silica Sol (Projection Formation Agent Liquid)

Colloidal silica (average particle size: 120 nm): 2.0 parts

Methyl ethyl ketone: 1.4 parts

Other Components

Stearic acid: 2.0 parts

Stearic acid amide: 0.2 parts

Butyl stearate: 2.0 parts

Polyisocyanate (CORONATE (registered product) L manufactured by Tosoh Corporation): 2.5 parts

Finishing Additive Solvent

Cyclohexanone: 200.0 parts

Methyl ethyl ketone: 200.0 parts

Non-Magnetic Layer Forming Composition

α-Iron oxide powder (average particle volume: see Table 1): 80.0 parts

Carbon black (average particle size: 20 nm, pH: see Table 1): 20.0 parts

Electron ray curable vinyl chloride copolymer: 13.0 parts

Electron beam curable polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Cyclohexanone: 140.0 parts

Methyl ethyl ketone: 170.0 parts

Butyl stearate: 2.0 parts Stearic acid: 1.0 part

Back Coating Layer Forming Composition

Non-magnetic inorganic powder (α-iron oxide powder): 80.0 parts

(Average particle size: 0.15 μm, average acicular ratio: 7, BET specific surface area:

52 m²/g)

Carbon black (average particle size: 20 nm): 20.0 parts

Carbon black (average particle size: 100 nm): 3.0 parts

A vinyl chloride copolymer: 13.0 parts

A sulfonic acid group-containing polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Cyclohexanone: 140.0 parts

Methyl ethyl ketone: 170.0 parts

Stearic acid: 3.0 parts

Polyisocyanate (CORONATE (registered product) L manufactured by Tosoh Corporation): 5.0 parts

Methyl ethyl ketone: 400.0 parts

Preparation of Each Layer Forming Composition

The magnetic layer forming composition was prepared by the following method.

The magnetic liquid was prepared by dispersing (beads-dispersing) the component by using a batch type vertical sand mill for 24 hours. As dispersion beads, zirconia beads having a bead diameter of 0.5 mm were used. The prepared magnetic liquid, the abrasive solution, and other components (silica sol, other components, and finishing additive solvent) were mixed with each other and beads-dispersed for 5 minutes by using the sand mill, and the treatment (ultrasonic dispersion) was performed with a batch type ultrasonic device (20 kHz, 300 W) for 0.5 minutes. After that, the obtained mixed solution was filtered by using a filter having a hole diameter of 0.5 μm, and the magnetic layer forming composition was prepared.

The non-magnetic layer forming composition was prepared by the following method.

The components excluding the lubricant (butyl stearate and stearic acid) were kneaded and diluted with an open kneader, and then dispersed with a transverse beads mill disperser. Then, the lubricant (butyl stearate and stearic acid) was added, and the mixture was stirred and mixed with a dissolver stirrer to prepare a non-magnetic layer forming composition.

The back coating layer forming composition was prepared by the following method.

The components excluding the lubricant (stearic acid), polyisocyanate, and methyl ethyl ketone (400.0 parts) were kneaded and diluted with an open kneader, and then dispersed with a transverse beads mill disperser. Then, the lubricant (stearic acid), polyisocyanate, and methyl ethyl ketone (400.0 parts) were added, and the mixture was stirred and mixed with a dissolver stirrer to prepare a back coating layer forming composition.

Manufacturing of Magnetic Tape and Magnetic Tape Cartridge

The non-magnetic layer forming composition was applied to a biaxial stretching support made of polyethylene naphthalate having a thickness of 4.1 μm so that the thickness after the drying is 0.7 μm and was dried to emit an electron ray to have energy of 40 kGy at an acceleration voltage of 125 kV. The magnetic layer forming composition was applied onto that so that the thickness after the drying is 0.1 μm and dried, and the back coating layer forming composition was applied to a surface of the support opposite to the surface where the non-magnetic layer and the magnetic layer are formed, so that the thickness after the drying is 0.3 μm and dried.

Then, a calender process was performed by using a 7-stage calender roll configured of only a metal roll, at a calendar speed of 80 m/min, linear pressure of 294 kN/m, and a calender temperature (surface temperature of a calender roll) of 80° C. Then, the heat treatment was performed in the environment of the ambient temperature of 70° C. for 36 hours. After the heat treatment, slitting is performed to have a width of ½ inches.

The surface of the magnetic layer of the magnetic tape having a width of ½ inches thus obtained was subjected to the burnishing process and the wiping process. The burnishing process and the wiping process were performed in a process device having a configuration shown in FIG. 1 of JP-H06-52544A, by using a commercially available abrasive tape (product name MA22000 manufactured by Fujifilm Holdings Corporation, abrasive: diamond/Cr₂O₃/α-iron oxide) as an abrasive tape, by using a commercially available sapphire blade (manufactured by Kyocera Corporation, width of 5 mm, length of 35 mm, an angle of a distal end of 60 degrees) as a blade for grinding, and by using a commercially available wiping material (product name WRP736 manufactured by Kuraray Co., Ltd.) as a wiping material. For the process conditions, the process conditions in Example 12 of JP-H06-52544A was used, except that the burnishing process tensions during the burnishing process on the central region and the region in the vicinity of the edge of the surface of the magnetic layer were set to values described in Table 1.

After that, by recording a servo signal on a magnetic layer of the obtained magnetic tape with a commercially available servo writer, and including a servo pattern (timing-based servo pattern) having the disposition and shape according to the linear tape-open (LTO) Ultrium format on the servo band was obtained.

Accordingly, a magnetic tape including data bands, servo bands, and guide bands in the disposition according to the LTO Ultrium format in the magnetic layer, and including servo patterns (timing-based servo pattern) having the disposition and the shape according to the LTO Ultrium format on the servo band was obtained. The servo pattern formed by doing so is a servo pattern disclosed in Japanese Industrial Standards (JIS) X6175:2006 and Standard ECMA-319 (June 2001).

The total number of servo bands is five, and the total number of data bands is four.

A magnetic tape (length of 960 m) on which the servo signal was recorded as described above was wound around the reel of the magnetic tape cartridge (LTO Ultrium 8 data cartridge), and a leader tape according to Article 9 of Section 3 of standard European Computer Manufacturers Association (ECMA)-319 (June 2001) was bonded to an end thereof by using a commercially available splicing tape.

By doing so, a magnetic tape cartridge in which the magnetic tape was wound around the reel was manufactured.

Examples 2 to 24 and Comparative Examples 1 to 10

A magnetic tape and a magnetic tape cartridge were obtained by the method described in Example 1, except that the items shown in Table 1 were changed as shown in Table 1.

For Examples 18 to 24, the step after recording the servo signal was changed as follows. That is, the heat treatment was performed after recording the servo signal. On the other hand, in Examples 1 to 17 and Comparative Examples 1 to 10, since such heat treatment was not performed, “None” was shown in the column of “heat treatment condition” in Table 1.

For Examples 18 to 24, the magnetic tape (length of 970 m) after recording the servo signal as described in Example 1 was wound around a core for the heat treatment and heat-treated in a state of being wound around the core. As the core for heat treatment, a solid core member (outer diameter: 50 mm) formed of a resin and having a value of a bending elastic modulus shown in Table 1 was used, and the tension in a case of the winding was set as a value shown in Table 1. The heat treatment temperature and heat treatment time in the heat treatment were set to values shown in Table 1. The weight absolute humidity in the atmosphere in which the heat treatment was performed was 10 g/kg Dry air.

After the heat treatment, the magnetic tape and the heat treatment core were sufficiently cooled, and then the magnetic tape was detached from the heat treatment core and wound around a core for temporary winding. As the core for temporary winding, a solid core member having the same outer diameter and formed of the same material as the core for heat treatment was used, and the tension at the time of winding was set as 0.6 N.

After that, the magnetic tape having the final product length (960 m) was wound around the reel of the magnetic tape cartridge (LTO Ultrium 8 data cartridge) from the core for temporary winding, the remaining length of 10 m was cut out, and a leader tape according to Article 9 of Section 3 of standard European Computer Manufacturers Association (ECMA)-319 (June 2001) was bonded to an end of a cut side thereof by using a commercially available splicing tape.

By doing so, a magnetic tape cartridge in which the magnetic tape was wound around the reel was manufactured.

For each of the Examples and Comparative Examples, four magnetic tape cartridges were manufactured, one was used for the evaluation of running stability below, and the other three were used for the evaluations (1) to (3) of the magnetic tape.

Evaluation of Running Stability

In an environment with a temperature of 40° C. and a relative humidity of 10%, the running stability was evaluated by the following method.

The temperature and the humidity described above are examples of the temperature and the humidity in the high temperature and low humidity environment. In addition, the following head tilt angle is used as an exemplary value of an angle that can be used in a case of performing the recording and/or reproducing of data at different head tilt angles. Therefore, the temperature and the humidity of the environment and the head tilt angle in a case of performing the recording of the data on the magnetic tape and the reproducing of the recorded data according to one aspect of the present invention are not limited to the above values and the following values.

Using each of the magnetic tape cartridges of the examples and the comparative examples, data recording and reproducing were performed using the magnetic tape device having the configuration shown in FIG. 8 . The arrangement order of the modules included in the recording and reproducing head mounted on the recording and reproducing head unit is “recording module-reproducing module-recording module” (total number of modules: 3). The number of magnetic head elements in each module is 32 (Ch0 to Ch31), and the element array is configured by sandwiching these magnetic head elements between the pair of servo signal reading elements. The reproducing element width of the reproducing element included in the reproducing module is 0.8 μm.

By the following method, the performing of the recording and reproducing of data and evaluating of the running stability during the reproducing were performed four times in total by sequentially changing the head tilt angle in the order of 0°, 15°, 30°, and 45°. The head tilt angle is an angle θ formed by the axis of the element array of the reproducing module with respect to the width direction of the magnetic tape at the start of each time of running. The angle θ was set by the control device of the magnetic tape device at the start of each time of running of the magnetic tape, and the head tilt angle was fixed during each time of running of the magnetic tape.

The magnetic tape cartridge was set in the magnetic tape device and the magnetic tape was loaded. Next, while performing servo tracking, the recording and reproducing head unit records pseudo random data having a specific data pattern on the magnetic tape. The tension applied in the tape longitudinal direction at that time is a constant value. At the same time with the recording of the data, the value of the servo band spacing of the entire tape length was measured every 1 m of the longitudinal position and recorded in the cartridge memory.

Next, while performing servo tracking, the recording and reproducing head unit reproduces the data recorded on the magnetic tape. The tension applied in the tape longitudinal direction at that time is a constant value.

The running stability was evaluated using a standard deviation of a reading position PES (Position Error Signal) in the width direction based on the servo signal obtained by the servo signal reading element during the reproducing (hereinafter, referred to as “σPES”) as an indicator.

PES is obtained by the following method.

In order to obtain the PES, the dimensions of the servo pattern are required. The standard of the dimension of the servo pattern varies depending on generation of LTO. Therefore, first, an average distance AC between the corresponding four stripes of the A burst and the C burst and an azimuth angle α of the servo pattern are measured using a magnetic force microscope or the like.

An average time between 5 stripes corresponding to the A burst and the B burst over the length of 1 LPOS word is defined as a. An average time between 4 stripes corresponding to the A burst and the C burst over the length of 1 LPOS word is defined as b. At this time, the value defined by AC×(½−a/b)/(2×tan(α)) represents a reading position PES (Position Error Signal) in the width direction based on the servo signal obtained by the servo signal reading element over the length of 1 LPOS word. Regarding the magnetic tape, an end on a side wound around a reel of the magnetic tape cartridge is referred to as an inner end, an end on the opposite side thereof is referred to as an outer end, the outer end is set to 0 m, and in a region in a tape longitudinal direction over a length of 30 m to 200 m, the standard deviation of PES (σPES) obtained by the method described above was calculated.

The arithmetic average of σPES obtained during four times of recording and reproducing in total is shown in the column of “σPES” in Table 1. In a case where the σPES is less than 70 nm, it can be determined that the running stability is excellent.

Evaluation of Magnetic Tape

(1) Edge Portion Ra, Central Portion Ra, Ra Ratio (Central Portion Ra/Edge Portion Ra)

The magnetic tape was extracted from each of the magnetic tape cartridges of Examples and Comparative Examples, the edge portion Ra and the central portion Ra were obtained by the method described above, and the Ra ratio (central portion Ra/edge portion Ra) was calculated from the obtained values.

(2) Standard Deviation of Curvature of Magnetic Tape in Longitudinal Direction

The magnetic tape was taken out from the magnetic tape cartridge, and the standard deviation of the curvature of the magnetic tape in the longitudinal direction was determined by the method described above.

(3) Tape Thickness

10 tape samples (length: 5 cm) were cut out from any part of the magnetic tape extracted from each of the magnetic tape cartridges of Examples and Comparative Examples, and these tape samples were stacked to measure the thickness. The thickness was measured using a digital thickness gauge of a Millimar 1240 compact amplifier manufactured by MARH and a Millimar 1301 induction probe. The value (thickness per tape sample) obtained by calculating 1/10 of the measured thickness was defined as the tape thickness. For all of the magnetic tape, the tape thickness was 5.2 μm.

The result described above is shown in Table 1 (Tables 1-1 and 1-2).

TABLE 1-1 Magnetic layer forming composition Ra Heat treatment conditions Stan- Burnishing ratio Non-magnetic layer Ten- dard process Central α-iron bend- sion devi- tension [gf] Ra (nm) portion oxide ing during ation Region Cen- Edge Ra/ powder Car- elastic wind- of cur- Ferro- Cen- in tral por- edge Average bon mod- ing vature magnetic tral vicinity portion tion portion particle black Temper- ulus around (mm/ σPES powder region of edge Ra Ra Ra volume pH ature Time of core core m) (nm) Example 1 BaFe 122 100 1.12 1.50 0.75 2.0 × 10⁻⁶ μm³ 5.0 None None None None 6 54 Example 2 BaFe 111 100 1.30 1.50 0.87 2.0 × 10⁻⁶ μm³ 5.0 None None None None 6 53 Example 3 BaFe 111 107 1.30 1.37 0.95 2.0 × 10⁻⁶ μm³ 5.0 None None None None 6 54 Example 4 BaFe 124 111 1.10 1.30 0.85 2.0 × 10⁻⁶ μm³ 5.0 None None None None 6 53 Example 5 BaFe 131 117 1.00 1.20 0.83 2.0 × 10⁻⁶ μm³ 5.0 None None None None 6 53 Example 6 BaFe 156 131 0.75 1.00 0.75 2.0 × 10⁻⁶ μm³ 5.0 None None None None 6 52 Example 7 BaFe 156 140 0.75 0.90 0.83 2.0 × 10⁻⁶ μm³ 5.0 None None None None 6 53 Example 8 BaFe 156 151 0.75 0.79 0.95 2.0 × 10⁻⁶ μm³ 5.0 None None None None 6 52 Example 9 BaFe 233 210 0.30 0.40 0.75 2.0 × 10⁻⁶ μm³ 5.0 None None None None 6 53 Example 10 BaFe 233 228 0.30 0.32 0.94 2.0 × 10⁻⁶ μm³ 5.0 None None None None 6 52 Example 11 BaFe 150 131 0.70 0.90 0.78 1.0 × 10⁻⁶ μm³ 5.0 None None None None 6 46 Example 12 BaFe 156 140 0.65 0.80 0.81 1.0 × 10⁻⁶ μm³ 5.0 None None None None 6 44 Example 13 BaFe 156 151 0.65 0.69 0.94 1.0 × 10⁻⁶ μm³ 5.0 None None None None 6 45 Example 14 BaFe 156 140 0.65 0.80 0.81 1.0 × 10⁻⁶ μm³ 5.0 None None None None 6 42 Example 15 BaFe 156 151 0.65 0.69 0.94 1.0 × 10⁻⁶ μm³ 5.0 None None None None 6 43 Example 16 BaFe 156 140 0.60 0.75 0.80 1.0 × 10⁻⁶ μm³ 3.5 None None None None 6 35 Example 17 BaFe 145 141 0.70 0.74 0.95 1.0 × 10⁻⁶ μm³ 3.5 None None None None 6 34 Example 18 BaFe 156 140 0.60 0.75 0.80 1.0 × 10⁻⁶ μm³ 3.5 50° C. 5 0.8 0.6N 5 33 hours GPa Example 19 BaFe 156 140 0.60 0.75 0.80 1.0 × 10⁻⁶ μm³ 3.5 60° C. 5 0.8 0.6N 4 33 hours GPa Example 20 BaFe 156 140 0.60 0.75 0.80 1.0 × 10⁻⁶ μm³ 3.5 70° C. 5 0.8 0.6N 3 32 hours GPa Example 21 BaFe 156 140 0.60 0.75 0.80 1.0 × 10⁻⁶ μm³ 3.5 70° C. 15 0.8 0.8N 2 30 hours GPa Example 22 SrFe1 111 100 1.15 1.35 0.85 1.0 × 10⁻⁶ μm³ 3.5 70° C. 15 0.8 0.8N 2 30 hours GPa Example 23 SrFe2 111 100 1.15 1.35 0.80 1.0 × 10⁻⁶ μm³ 3.5 70° C. 15 0.8 0.8N 2 30 hours GPa Example 24 ε-iron 111 100 1.15 1.35 0.85 1.0 × 10⁻⁶ μm³ 3.5 70° C. 15 0.8 0.8N 2 30 oxide hours GPa powder

TABLE 1-2 Magnetic layer forming composition Ra Heat treatment conditions Stan- Burnishing ratio Non-magnetic layer Ten- dard process Central α-iron bend- sion devi- tension [gf] Ra (nm) portion oxide ing during ation Region Cen- Edge Ra/ powder Car- elastic wind- of cur- Ferro- Cen- in tral por- edge Average bon mod- ing vature magnetic tral vicinity portion tion portion particle black Temper- ulus around (mm/ σPES powder region of edge Ra Ra Ra volume pH ature Time of core core m) (nm) Comparative BaFe 100 100 1.60 1.60 1.00 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 80 Example 1 Comparative BaFe 105 105 1.50 1.50 1.00 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 86 Example 2 Comparative BaFe 117 117 1.30 1.30 1.00 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 90 Example 3 Comparative BaFe 100 117 1.60 1.30 1.23 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 87 Example 4 Comparative BaFe 111 117 1.40 1.30 1.08 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 88 Example 5 Comparative BaFe 117 100 1.30 1.60 0.81 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 83 Example 6 Comparative BaFe 140 162 1.00 0.80 1.25 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 85 Example 7 Comparative BaFe 175 175 0.70 0.70 1.00 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 86 Example 8 Comparative BaFe 175 140 0.70 1.00 0.70 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 90 Example 9 Comparative BaFe 300 280 0.20 0.25 0.80 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 93 Example 10

From the results shown in Table 1, it can be confirmed that the magnetic tape of the examples showed excellent running stability in a case where the magnetic tape was caused to run at different head tilt angles in the high temperature and low humidity environment.

The magnetic tape cartridge was manufactured by the method described in Example 1, except that, during the manufacturing of the magnetic tape, after forming the coating layer by applying the magnetic layer forming composition, a homeotropic alignment process was performed by applying a magnetic field having a magnetic field strength of 0.3 T in a vertical direction with respect to a surface of a coating layer, while the coating layer of the magnetic layer forming composition is wet, and then, the drying was performed to form the magnetic layer.

A sample piece was cut out from the magnetic tape taken out from the magnetic tape cartridge. For this sample piece, a vertical squareness ratio was obtained by the method described above using a TM-TRVSM5050-SMSL type manufactured by Tamagawa Seisakusho Co., Ltd. as an oscillation sample type magnetic-flux meter and it was 0.60.

The magnetic tape was also taken out from the magnetic tape cartridge of Example 1, and the vertical squareness ratio was obtained in the same manner for the sample piece cut out from the magnetic tape, and it was 0.55.

The magnetic tapes taken out from the above two magnetic tape cartridges were attached to each of the ½-inch reel testers, and the electromagnetic conversion characteristics (signal-to-noise ratio (SNR)) were evaluated by the following methods. As a result, regarding the magnetic tape manufactured by performing the homeotropic alignment process, a value of SNR 2 dB higher than that of the magnetic tape manufactured without the homeotropic alignment process was obtained.

In an environment of a temperature of 23° C. and a relative humidity of 50%, a tension of 0.7 N was applied in the longitudinal direction of the magnetic tape, and recording and reproduction were performed for 10 passes. A relative speed of the magnetic head and the magnetic tape was set as 6 m/sec. The recording was performed by using a metal-in-gap (MIG) head (gap length of 0.15 μm, track width of 1.0 μm) as the recording head and by setting a recording current as an optimal recording current of each magnetic tape. The reproduction was performed using a giant-magnetoresistive (GMR) head (element thickness of 15 nm, shield interval of 0.1 μm, reproducing element width of 0.8 μm) as the reproduction head. The head tilt angle was set to 0°. A signal having a linear recording density of 300 kfci was recorded, and the reproduction signal was measured with a spectrum analyzer manufactured by ShibaSoku Co., Ltd. In addition, the unit kfci is a unit of linear recording density (cannot be converted to SI unit system). As the signal, a sufficiently stabilized portion of the signal after starting the running of the magnetic tape was used.

One aspect of the invention is advantageous in a technical field of various data storages. 

What is claimed is:
 1. A magnetic tape comprising: a non-magnetic support; and a magnetic layer containing a ferromagnetic powder, wherein an edge portion Ra which is an arithmetic average roughness Ra measured at an edge portion of a surface of the magnetic layer is 1.50 nm or less, a central portion Ra which is an arithmetic average roughness Ra measured at a central portion of the surface of the magnetic layer is 0.30 nm to 1.30 nm, and a Ra ratio (central portion Ra/edge portion Ra) is 0.75 to 0.95.
 2. The magnetic tape according to claim 1, further comprising: a non-magnetic layer containing a non-magnetic powder between the non-magnetic support and the magnetic layer.
 3. The magnetic tape according to claim 2, wherein the non-magnetic powder contains a Fe-based inorganic oxide powder having an average particle volume of 2.0×10⁻⁶ μm³ or less.
 4. The magnetic tape according to claim 2, wherein the non-magnetic powder contains carbon black having a pH of 5.0 or less.
 5. The magnetic tape according to claim 2, wherein the non-magnetic powder contains a Fe-based inorganic oxide powder having an average particle volume of 2.0×10⁻⁶ μm³ or less and carbon black having a pH of 5.0 or less.
 6. The magnetic tape according to claim 2, wherein the non-magnetic powder contains a Fe-based inorganic oxide powder having an average particle volume of 2.0×10⁻⁶ μm³ or less and carbon black having a pH of 5.0 or less, and a standard deviation of curvature of the magnetic tape in a longitudinal direction is 5 mm/m or less.
 7. The magnetic tape according to claim 2, wherein the non-magnetic powder contains a Fe-based inorganic oxide powder having an average particle volume of 2.0×10⁻⁶ μm³ or less and carbon black having a pH of 5.0 or less, a standard deviation of curvature of the magnetic tape in a longitudinal direction is 5 mm/m or less, a tape thickness is 5.2 μm or less, and a vertical squareness ratio of the magnetic tape is 0.60 or more.
 8. The magnetic tape according to claim 1, wherein a standard deviation of curvature of the magnetic tape in a longitudinal direction is 5 mm/m or less.
 9. The magnetic tape according to claim 1, further comprising: a back coating layer containing a non-magnetic powder on a surface side of the non-magnetic support opposite to a surface side provided with the magnetic layer.
 10. The magnetic tape according to claim 1, wherein a tape thickness is 5.2 μm or less.
 11. The magnetic tape according to claim 1, wherein a vertical squareness ratio of the magnetic tape is 0.60 or more.
 12. A magnetic tape cartridge comprising: the magnetic tape according to claim
 1. 13. A magnetic tape device comprising: the magnetic tape according to claim
 1. 14. The magnetic tape device according to claim 13, further comprising: a magnetic head, wherein the magnetic head includes a module including an element array having a plurality of magnetic head elements between a pair of servo signal reading elements, and the magnetic tape device changes an angle θ formed by an axis of the element array with respect to a width direction of the magnetic tape during running of the magnetic tape in the magnetic tape device. 